Reducing immunogenicity to pegloticase

ABSTRACT

The disclosure provides methods of treating gout in patients comprising administering a PEGylated uricase. Also provided are methods of treating gout in patients comprising co-administering a PEGylated uricase and methotrexate (MTX). Also provided are methods of reducing immunogenicity of a PEGylated uricase and prolonging the urate lowering effect comprising co-administration of the PEGylated uricase and MTX.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Patent Application No. 62/798,786, filed Jan. 30, 2019, U.S. Provisional Patent Application No. 62/855,519, filed May 31, 2019, and U.S. Provisional Patent Application No. 62/903,570 filed Sep. 20, 2019, which are incorporated by reference herein in their entireties.

FIELD OF THE DISCLOSURE

Gout affects approximately 4% of the U.S. population, is the most common form of inflammatory arthritis in men, and is associated with decreased quality of life. The frequency of gout is increasing worldwide, with prevalence rates estimated to be as high as 7% in older men. It is estimated that up to 400,000 (up to 5% of the estimated 8 million persons with gout) in the United States experience chronic refractory gout, characterized by ongoing symptoms of active disease and a failure to control/maintain serum urate <6 mg/dL with conventional xanthine oxidase inhibitors (i.e., allopurinol and febuxostat) and uricosuric agents (i.e., probenecid). These patients often have significant, disabling urate deposits in soft tissues and bone known as tophi.

Uric acid (UA) is the end metabolite in the human purine catabolic pathway. When the concentration of serum uric acid (SUA) is above the biochemical limit of solubility, 6.8 mg/dL, monosodium urate crystals may precipitate in tissues. It is hypothesized that after many years of persistent hyperuricemia, accumulation of monosodium urate crystals causes symptoms of gout, such as acute inflammation of joints (gout flare), formation of gout tophi, gouty arthritis, and UA nephropathy (including UA renal stones). Control of chronic gout cannot be achieved without maintaining SUA <6 mg/dL. A total of 8.3 million patients have been diagnosed with gout in the United States. The principal pharmaceutical approach to the treatment of gout is the use of the xanthine oxidase inhibitors, allopurinol, and febuxostat, to block the synthesis of UA. Approximately 2% of patients treated with allopurinol develop allergic reactions and a severe hypersensitivity syndrome occurs in about 0.4% of the patients. Patients with medical contraindications to xanthine oxidase inhibitors because of allergy/hypersensitivity, or who have failed to normalize SUA at maximum medically appropriate doses of these medications, can go on to develop chronic gout.

Pegloticase or PEGylated uricase (KRYSTEXXA®; “KXX”) is a monomethoxypoly(ethylene glycol) (PEG) modified recombinant mammalian uricase (urate oxidase) which reduces levels of UA in the serum (or plasma) by catalyzing its conversion to allantoin, a water-soluble metabolite more readily excreted in the urine than uric acid. Pegloticase provides a new therapeutic mechanism to reduce SUA in patients with chronic gout refractory to conventional oral therapy. These patients experience a severe burden of gout disease characterized by tophi (approximately 70%), frequent and often crippling flares (approximately 7 per year), and deforming arthritis. Pegloticase provides medical benefits in patients who respond by lowering SUA and by reducing tophus burden in these patients who currently have no therapeutic options.

Seven clinical studies have been conducted with pegloticase in patients with refractory chronic gout. The Phase 1 program established an acceptable profile of tolerability and safety for intravenous (IV) dosing, whereas subcutaneous dose administration was less well tolerated. The Phase 2 program identified a minimally effective dose (4 mg), a dose-response plateau dose (12 mg), a safe and optimally effective dose (8 mg), and a once every 2 weeks or once every 4 weeks dosing regimen.

Two randomized, double-blind, placebo-controlled, multi-center, 6-month safety and efficacy Phase 3 studies have been conducted in a total of 225 hyperuricemic patients (SUA >8 mg/dL) with symptomatic gout who reported contraindication to or who had failed to normalize SUA with allopurinol therapy. The pooled efficacy results showed improvements in tophus burden consistent with urate-lowering effect of pegloticase in both dose groups. Improvements were more rapid in patients who received pegloticase 8 mg every 2 weeks compared to every 4 weeks and met the outcomes data of complete resolution of at least 1 tophus with no new or progressive tophi as assessed by blinded assessment of digital photographs of target tophi.

The pooled safety results from these Phase 3 studies showed that gout flares were more common in the pegloticase groups than in the placebo group during the first 3 months of therapy, a physiological effect resulting from SUA-lowering which is commonly observed upon the initiation of all urate-lowering therapies. During the second 3 months of treatment, a lower proportion of pegloticase-treated patients experienced flares than patients receiving placebo. The incidence of flares during this period was lowest in the group receiving pegloticase 8 mg every 2 weeks than in the group who received pegloticase 8 mg every 4 weeks, as was the incidence of infusion-related reactions (26% with biweekly dosing vs. 40% with the every-4-week dosing regimen). Both infusion reactions (IRs) and gout flares were least common in patients with sustained urate-lowering responses to treatment and those who received bi-weekly treatment. In most pegloticase-treated patients with IRs, a loss of response to pegloticase (return to SUA >6 mg/dL) preceded the time of the first IR (20/21; 95%).

A relationship between the loss of urate-lowering efficacy, incidence of IRs, and high-titer antibody formation was identified in a post-hoc analysis of the pooled data from the Phase 3 studies. Patients with high anti-pegloticase antibody titers (>1:2430) showed a loss of pegloticase activity attributed to a more rapid clearance of drug in the presence of these antibodies. In one study, 69 (41%) of 169 patients receiving pegloticase developed high titer anti-pegloticase antibodies and subsequently lost response to the drug. In a second study, only 1 of 52 participants with high antibody titers maintained a response to pegloticase (serum urate <6 mg/dL). In addition, 60% participants with high titers developed IR. Anti-pegloticase antibodies were largely directed to the polyethylene glycol (PEG) portion of the molecule and altered the pharmacokinetic clearance of pegloticase, resulting in inhibition of SUA lowering activity. In another study, only 7 of 65 patients (10.8%) with an antibody titer exceeding 1:2430 at any time during treatment maintained a response to pegloticase compared with 89.2% (58/65) who had never had an antibody titer above that level. In addition, 31 of 52 (60%) patients with titers exceeding 1:2430 developed IRs. The ability of pegloticase to induce antibody production demonstrated the antigenic potential of the drug, and thus raised the possibility that relatively large or more frequent doses of pegloticase (antigen) might reduce antibody formation by induction of antigen-specific non-responsiveness (high zone tolerance). By preventing the formation of anti-pegloticase antibodies, a tolerizing dose regimen should prevent loss of response to the drug and decrease the incidence of IRs associated with it.

As described herein, an alternate approach to prevent immunogenicity by pegloticase and therefore reduce the incidence of IRs, as well as to enhance the response rate seen with pegloticase alone in adults with uncontrolled gout, is co-administration or concomitant administration of pegloticase and an immunosuppressive agent. As described herein, one such immunosuppressive agent is methotrexate (MTX) immunosuppressive therapy.

The long-term safety of pegloticase has been demonstrated in an open-label extension study that enrolled 151 patients: 149 received pegloticase either bi-weekly or every 4 weeks for up to 30 months and 2 chose observation only. No new safety signals were observed and ongoing patient benefit in several clinical outcome measures was maintained beyond the 6-month period of the double-blind studies.

In one aspect, the disclosure provides a method of treating gout in a patient having a serum uric acid level of ≥6 mg/dL comprising: administering MTX to said patient at a dose of 15 mg per week for a period of 4 weeks prior to the first administration of a PEGylated uricase; co-administering the PEGylated uricase and MTX to said patient using a dosage regimen comprising a dose of 8 mg of the PEGylated uricase intravenously every 2 weeks for a total of 26 doses; and a dose of 15 mg of MTX per week, wherein the co-administered MTX is administered concurrently with each administration of the PEGylated uricase.

In another aspect, the disclosure provides a method of reducing immunogenicity to a PEGylated uricase and prolonging the urate lowering effect comprising co-administration of the PEGylated uricase at a dosage of 8 mg intravenously every 2 weeks and MTX at a dosage of 15 mg per week to a patient having a serum uric acid level of ≥6 mg/dL prior to PEGylated uricase treatment initiation; wherein the co-administration of the PEGylated uricase and MTX result in the serum uric acid level being normalized relative to a patient not receiving co-administration of the PEGylated uricase and MTX immunosuppressive therapy.

In one embodiment, these methods further comprise an altered dosage of MTX, wherein the altered dosage comprises increasing folic acid; or dividing the dosage of MTX; or reducing the dosage of MTX, wherein the altered dosage of MTX is based on the development of laboratory findings as provided in Table 1. In another embodiment, a method as described herein further comprises a prophylactic regimen of colchicine for a period of at least 2 weeks prior to the first administration of the PEGylated uricase. In another embodiment, wherein the SUA levels of the patient are determined prior to each dose of the PEGylated uricase. In another embodiment, such a method further comprises measuring one or more of trough PEGylated uricase levels, anti-PEGylated uricase antibody levels, and anti-PEG antibody levels, prior to each dose of the PEGylated uricase after the first dose.

In another embodiment, any of such methods further comprises measuring serum uric acid (SUA) levels, hematology, and/or liver function tests on a weekly basis during treatment. In another embodiment, blood tests may be performed every other week, or every third week. For example, blood tests may be performed at screening, at weeks 0 (baseline), 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23. In another embodiment, blood tests may be performed for any purpose (i.e., hematology or clinical chemistry) at screening, baseline, week 12, and week 26. In some embodiments, a blood test as described herein may be performed on the same day each week or may be performed within 1 or 2 or 3 days of the previous blood test performed. Blood tests may be drawn for any blood tests described herein within 24 hours prior to administration of KXX or from about 1 to about 3 days prior to each KXX infusion.

For determination of serum uric acid, if the SUA is >6 mg/dL, the subject may not be dosed and the SUA may be repeated. In some embodiments, if the SUA is >6 mg/dL, a subject may be withdrawn from the study. In other embodiments, samples that result in discordant results between laboratories may be evaluated to discuss whether the subject should continue on the study drug or discontinue dosing.

In another embodiment, said co-administration of the PEGylated uricase and MTX results in normalization of the SUA level in the patient relative to a patient not receiving co-administration of the PEGylated uricase and MTX. In another embodiment, the SUA level is reduced to less than 6 mg/dL as a result of co-administration of the PEGylated uricase and MTX. In another embodiment, the SUA level is reduced to less than 5 mg/dL as a result of co-administration of the PEGylated uricase and MTX. In another embodiment, the SUA level is reduced to less than 2 mg/dL as a result of co-administration of the PEGylated uricase and MTX.

In another embodiment, the incidence of infusion reaction, gout flare, or anaphylaxis is reduced as a result of co-administration of the PEGylated uricase and MTX. In another embodiment, the level of MTX metabolite is increased relative to a patient not receiving co-administration of the PEGylated uricase and MTX.

In another embodiment, such a method further comprises measuring one or more of peripheral joint urate deposition volume and inflammatory volume via any advanced imaging technique. In another embodiment, peripheral joint urate deposition volume is reduced in the patient relative to a patient not receiving treatment using co-administration of the PEGylated uricase and MTX. In another embodiment, peripheral joint urate deposition volume is determined by dual-energy computed tomography (DECT) scanning. In another embodiment, peripheral joint urate deposition volume is determined by ultrasound.

In another embodiment, inflammatory volume is reduced in the patient relative to a patient not receiving treatment using co-administration of the PEGylated uricase and MTX. In another embodiment, inflammatory volume is determined by Dynamic Contrast Enhanced—Magnetic Resonance Imaging (DCE-MRI) or MRI without contrast, or both.

In another embodiment, the mean titer of anti-PEGylated uricase antibodies is less than or equal to 1:6000 as a result of co-administration of the PEGylated uricase and MTX treatment. In another embodiment, the serum uric acid level is normalized by week 12 after co-administration of the PEGylated uricase and MTX treatment begins.

These and other embodiments of the disclosure are described in detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a graph of the urate reducing efficacy of pegloticase.

DETAILED DESCRIPTION Overview

In one embodiment, the disclosure provides a method of treating gout in a patient having a serum uric acid level of ≥6 mg/dL comprising: administering methotrexate (MTX) to said patient at a dose of 15 mg per week for a period of 4 weeks prior to the first administration of a PEGylated uricase; co-administering the PEGylated uricase and MTX to said patient using a dosage regimen comprising a dose of 8 mg of the PEGylated uricase intravenously every 2 weeks for a total of 26 doses; and a dose of 15 mg MTX per week, wherein the co-administered MTX is administered concurrently with each administration of the PEGylated uricase. In another embodiment, the disclosure provides a method of reducing or preventing loss of response to a PEGylated uricase and prolonging the urate lowering effect comprising co-administration of the PEGylated uricase at a dosage of 8 mg intravenously every 2 weeks and MTX at a dosage of 15 mg per week to a patient having a serum uric acid level of ≥6 mg/dL prior to PEGylated uricase treatment initiation; wherein the administration of the PEGylated uricase and MTX result in the serum uric acid level being normalized relative to a patient not receiving co-administration of the PEGylated uricase and MTX immunosuppressive therapy. KRYSTYEXXA® (Pegloticase)

KRYSTEXXA® (“KXX,” pegloticase) is a uric acid specific enzyme, which is a PEGylated product that consists of recombinant modified mammalian urate oxidase (uricase) produced by a genetically modified strain of Escherichia coli. KXX is indicated for the treatment of chronic gout in patients that are refractory to conventional therapy. KXX® is described at least in U.S. Pat. Nos. 8,188,224; 7,811,800; 9,534,013; 6,576,235; 9,377,454; 6,783,965; as well as PCT Publ. No. WO 2018/089808, each of which is incorporated herein in its entirety. In some embodiments, non-mammalian uricases may be used as deemed appropriate, or a uricase from any species. In other embodiments, muteins of a uricase as described herein, having an altered amino acid sequence, may be used and are encompassed within the present disclosure.

Certain uricases are useful for preparing conjugates with various forms of poly(ethylene glycol) or poly(ethylene oxide) (both referred to as PEG) to produce therapeutically efficacious forms of uricase having increased protein half-life and reduced immunogenicity. Thus, in some embodiments, uricase is covalently conjugated to monomethoxypoly(ethylene glycol) [mPEG] (10 kDa molecular weight). The cDNA coding for uricase is based on mammalian sequences. Each uricase subunit has a molecular weight of approximately 34 kDa per subunit. The average molecular weight of pegloticase (tetrameric enzyme conjugated to mPEG) is approximately 540 kDa.

In some embodiments, a uricase as described herein may be conjugated to any desired number of PEG or mPEG molecules, such as 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, or the like. In other embodiments, a uricase as described herein may be conjugated to other modifiers in addition to, or alternatively to, PEG or mPEG. Such PEG or mPEG molecules may be attached to a uricase using any means appropriate in accordance with the disclosure. For example, a PEG or mPEG molecule may be conjugated to a uricase as described herein by a cysteine residue, or a serine residue, or a lysine residue. A PEG or mPEG may be attached to a uricase as described herein using any specific amino acid in accordance with the disclosure.

In other embodiments, a uricase of the present disclosure may be modified with a non-PEG modification. For example, one or more residues of proline, alanine, and/or serine (PAS), or combinations thereof, referred to herein as PASylation. In other embodiments, a uricase as described herein may be modified by conjugation with an antibody, a protein, or a small molecule, or may be conjugated to poly(2-ethyl-2-oxazoline) referred to herein as POZylation. In other embodiments, a uricase may be modified at the amine end or the carboxy end, or both. In other embodiments, any other modifiers deemed appropriate may be used to extend the half-life in circulation in accordance with the present disclosure.

Mode of Action of KXX

KXX achieves its therapeutic effect by catalyzing the oxidation of uric acid to allantoin, thereby lowering serum uric acid. Allantoin is an inert and water-soluble purine metabolite. It is readily eliminated, primarily by renal excretion.

KXX (pegloticase) concentrations are expressed as concentrations of uricase protein. Each mL of KXX contains 8 mg of uricase protein (conjugated to 24 mg of 10 kDa mPEG), 2.18 mg Disodium Hydrogen Phosphate Dihydrate (Na₂HPO₄.2H₂O), 8.77 mg Sodium Chloride (NaCl), 0.43 mg Sodium Dihydrogen Phosphate Dihydrate (NaH₂PO₄.2H₂O), and Water for Injection to deliver 8 mg of pegloticase (as uricase protein).

KXX was granted orphan designation by the FDA on February 21, 2001 (ODA #00-1356) and KXX 8 mg every 2 weeks by IV infusion was approved by the United States (US) FDA on Sep. 14, 2010 for the treatment of adult patients with chronic gout refractory to conventional therapy. Since pegloticase was approved in the US, there have been no new safety signals reported to Horizon Pharma, PLC (Horizon) the manufacturer of KXX. The most common adverse events continue to be IRs, anaphylaxis, and gout flares. Post-marketing safety information suggests that the concomitant use of pegloticase with urate-lowering agents may mask the detection of patients who have lost therapeutic response to the drug and increase the risk of IR and/or anaphylaxis. Pegloticase is contraindicated in patients with glucose-6-phosphate dehydrogenase (G6PD) deficiency because of the risk of hemolysis and methemoglobinemia.

Treatment of Patients with KXX

KXX treatment may be initiated with monitoring of SUA levels prior to each infusion. In some embodiments, KXX therapy may be discontinued if the SUA levels increase to above 6 mg/dL, particularly when 2 consecutive levels above 6 mg/dL are observed, or when SUA levels at 2 consecutive visits are above 6 mg/dL.

In addition, to reduce the incidence of infusion reactions, adverse events (AEs), such as gout flare, or serious adverse events (SAEs) such as anaphylaxis, patients may be pre-medicated with antihistamines and/or corticosteroids. AEs and SAEs are described in detail below. Anaphylaxis or other IRs may occur with any infusion, including a first infusion, or any subsequent infusion, and generally manifests within 2 hours of the infusion. Delayed-type hypersensitivity reactions may also occur. The most common adverse reactions (occurring in about 5% or more of KXX-treated patients) are gout flares, infusion reactions, nausea, contusion or ecchymosis, nasopharyngitis, constipation, chest pain, anaphylaxis, and vomiting. Additional monitoring of patients during and after infusion may be beneficial to prevent or detect such reactions. In some embodiments, patients are monitored for one hour or more following administration of KXX. In some embodiments, gout flare prophylaxis may be recommended for patients when treating with KXX. For example, gout flare prophylaxis may be recommended for a period of about the first six months of KXX therapy.

In some embodiments, patients or subjects receiving KXX therapy, either alone or co-administered with an immunosuppressive agent, may experience exacerbation of congestive heart failure. For such patients, close monitoring after infusion may be beneficial.

In some embodiments, and to prevent or manage reactions to KXX therapy, such as anaphylaxis and/or infusion reactions, KXX may be administered in a healthcare setting and by a healthcare provider. The KXX admixture may be administered by intravenous infusion over a minimum of 120 minutes via gravity feed, syringe-type pump, or infusion pump. As described in detail below, KXX may be administered alone to a patient, or may be co-administered to a patient or subject with an immunosuppressive agent such as methotrexate (MTX). In some embodiments, KXX may be administered in a healthcare setting as described herein, and an immunosuppressive agent may be administered at home. In other embodiments, both KXX and an immunosuppressive agent such as MTX may be administered in a healthcare setting.

In some embodiments, pre-screening of patients or subjects to be administered KXX, either alone of co-administered with an immunosuppressive agent, such as MTX, for the presence of, or a risk for developing glucose-6-phosphate dehydrogenase (G6PD) deficiency may be beneficial. Such patients may be excluded from treatment with KXX because of a risk of hemolysis and/or methemoglobinemia.

In some embodiments, KXX, either alone, or in combination with an immunosuppressive agent or therapy, may be used to treat a patient with gout as described herein.

Dosage of KXX

In some embodiments, KXX may be administered at a dosage of 0.5 to 24 mg of uricase in solution every 2 to 4 weeks. The uricase may be administered in any appropriate way known to one of skill in the art, for example intravenously, intramuscularly or subcutaneously. In some embodiments, when the administration is intravenous, 0.5 to 12 mg of uricase is administered. In some embodiments, when the administration is subcutaneous, 4 to 24 mg of uricase is administered. In some embodiments, the uricase is administered by intravenous infusion over a 30- to 240-minute period. In some embodiments, 8 mg of uricase is administered once every two weeks. The recommended dose and regimen of KXX for adult patients is 8 mg (uricase protein) given as an intravenous (IV) infusion every two weeks. The optimal treatment duration with KXX has not been established. KXX is a sterile, clear, colorless solution containing 8 mg/mL pegloticase in phosphate-buffered saline, and it intended for intravenous infusion.

Dosage Forms of KXX

KXX may be provided in a 1-mL sterile concentrate for dilution containing 8 mg of pegloticase protein, expressed in uricase protein amounts.

Methotrexate (MTX)

It some embodiments, as described herein, KXX may be administered alone as a treatment, or may be co-administered with an immunosuppressive or immunomodulatory agent, such as MTX. In some embodiments, a course of MTX can mitigate immunogenicity to pegloticase, and/or enhance the response rate seen with pegloticase alone in adults with uncontrolled gout. In some embodiments, MTX may be administered to patients receiving KXX to prevent the formation of anti-KXX antibodies. Development of anti-KXX antibodies may increase the clearance of KXX, thereby causing loss of a drug response in the patient.

To the Inventors' knowledge, this was the first study to test the hypothesis that immunogenicity to pegloticase can be attenuated via MTX, and that the response rate seen with KXX alone in adults with uncontrolled gout can be enhanced by combining KXX with MTX. For this study, MTX was co-administered with KXX to patients or subjects to improve treatment efficacy and reduce IR in patients being treated for chronic refractory gout as an innovative approach to gout management with pegloticase. New strategies to deal with the growing burden of gout and to improve use of existing therapies are urgently needed and the present disclosure represents a novel approach addressing both clinical and immunological questions. In some embodiments, MTX may be administered for a specified period before KXX treatment begins (i.e., pre-dosing of MTX), which may be referred to herein as an MTX “lead-in” period. A lead-in period may begin, for example, 8 weeks, 7 weeks, 6 weeks, 5 weeks, 4 weeks, 3 weeks, 2 weeks, 1 week, 6 days, 5 days, 4 days, 3 days, 2 days, or 1 day prior to KXX treatment, at a dosage as described herein. In some embodiments, such a pre-dosing period may begin at week—4 (i.e., 4 weeks prior to KXX treatment begins) and continue for as long as deemed appropriate or beneficial. In some embodiments, an MTX lead-in period may continue from week -4 through day 1 of KXX treatment. In some embodiments, MTX may be administered after the lead-in period and for the duration of KXX treatment as described herein.

In some embodiments, MTX may be administered to the patient in any form, either orally or subcutaneously, and at any dose deemed appropriate by a clinician or practitioner. For subcutaneous administration, an auto-injector may be used by a patient or subject, or may be used by a clinician or practitioner. In some embodiments, oral MTX exposure plateaus at doses of greater than or equal to 15 mg/week. Thus, in some embodiments, the dosage of MTX used in the present study is 15 mg per week, administered orally. In other embodiments, MTX may be administered at a dosage of 15 mg per week, administered subcutaneously. One of skill in the art will understand that different routes of administration may be used without deviating from the scope of the disclosure.

Such a dosage may be administered to a patient to prevent or control immunogenicity to KXX or associated AEs, SAEs, or IRs occurring as a result of KXX treatment. In some embodiments, such a dosage may also be administered to enhance the response rate seen with pegloticase alone in adults with uncontrolled gout. In some embodiments, MTX may be administered to a patient starting when the serum uric acid level is greater than 6 mg/dL. Alternate dosages of MTX may be used as deemed appropriate by a clinician. For example, MTX may be administered at a dosage of 1.0 mg, 1.5 mg, 2.0 mg, 2.5 mg, 3.0 mg, 3.3 mg, 3.5 mg, 4.0 mg, 4.5 mg, 5.0 mg, 5.5 mg, 6.0 mg, 6.5 mg, 7.0 mg, 7.5 mg, 8.0 mg, 8.5 mg, 9.0 mg, 9.5 mg, 10.0 mg, 10.5 mg, 11.0 mg, 11.5 mg. 12.0 mg, 12.5 mg, 13.0 mg, 13.5 mg, 14.0 mg, 14.5 mg, 15.0 mg, 15.5 mg, 16.5 mg, 17.0 mg, 17.5 mg, 18.0 mg, 18.5 mg, 19.0 mg, 19.5 mg, 20.0 mg, 20.5 mg, 21.0 mg, 21.5 mg, 22.0 mg, 22.5 mg, 23.0 mg, 23.5 mg, 24.0 mg, 24.5 mg, 25 mg, 50 mg, 75 mg, 100 mg, 125 mg, 150 mg, 175 mg, 200 mg, or the like. In some embodiments, the dosage may be from 10 mg to 25 mg, 15 mg to 30 mg, 5 mg to 50 mg, or the like. In some embodiments, a maximum dose of 20 mg of MTX may be administered to a patient per week.

In some embodiments, MTX dosages may be altered or down-titrated as necessary in the event of gastrointestinal distress, central nervous system symptoms, or elevation in liver function tests. In some embodiments, for subjects experiencing adverse symptoms as described above, folic acid supplementation may be initiated or increased, or the dosage of MTX may be divided into two doses on the same day. In some embodiments, the dosage of MTX may be reduced to, for example, 10 mg in such subjects. In some embodiments, a temporary stop of MTX may be ordered for the patient or subject.

Table 1 below provides lab parameters that may be used to determine the dosage of MTX. The most common reasons to have a temporary stop are typically laboratory based (e.g., increased liver function tests, a decline in renal function, or a decline in white blood cells) or clinical, such as for gastrointestinal-related symptoms, infections, or other intolerance.

In some embodiments, if liver tests or renal tests become slightly abnormal or changed from baseline, the dosage of MTX may be reduced or temporarily stopped for 2-4 weeks. After re-evaluation of the laboratory tests, MTX may be restarted if appropriate. In other embodiments, a temporary stop of MTX may be ordered if an infection occurs, and maintained while the patient is on antibiotics, which is often 7-14 days unless the infection is severe. MTX may then be resumed if still clinically indicated.

For gastrointestinal symptoms or other tolerance issues, the dose of folic acid, which is given as a supplement to MTX to reduce side effects, may be reduced, or MTX may be held for 1-2 weeks if necessary.

TABLE 1 MTX Dose Guidance During Run-In Period and KXX + MTX Treatment Period Lab Parameters Value MIX Dose Change WBC  3.0 × 10⁹/L Decrease to 10 mg <3.0 × 10⁹/L Temporary stop Platelets  <50 × 10⁹/L Temporary stop Hematocrit <27% Temporary stop AST/ALT Between 1.5~2 × ULN Decrease to 10 mg   >2 × ULN Temporary stop eGFR <30 ml/min/1.73 m² Temporary stop New clinically Yes Temporary stop important symptoms/ signs*

In some embodiments, new clinically important symptoms or signs may also affect the dosage of MTX, such as rash or oral ulceration, persistent nausea, vomiting and diarrhea, new or increasing dyspnea or dry cough, or unexplained cough with fever, severe sore throat, abnormal bruising, severe headaches, fatigue, and problems concentrating, any other important medical events that might increase methotrexate toxicity or pre-dispose to new or worsening infection (e.g., undergoing surgery, hospitalization, being treated with antibiotics, having a clinical infection, developing new clinically significant pericardial/pleural effusion or ascites). In such cases, MTX may be temporarily stopped as deemed appropriate.

One of skill in the art will understand that dosages of drugs as described herein may be altered as needed for a patient or subject without deviating from the scope of the disclosure.

In other embodiments, MTX may be administered once per day, twice per day, 3 times per day, or more times per day as needed. In other embodiments, MTX may be administered every 2 days, or every 3 days, or every 4 days, or every 5 days, or every 6 days, or every 7 days, or every 8 days, or every 9 days, or every 10 days, or every 11 days, or every 12 days, or every 13 days, or every 14 days. In other embodiments, the drug may be administered one per week, twice per week, 3 times per week, 4 times per week, 5 times per week, 6 times per week, 7 times per week, 8 times per week, 9 times per week, 10 times per week, 11 times per week, 12 times per week, 13 times per week, 14 times per week, or the like. In some embodiments, different dosages or frequencies may be used on different days, as described herein.

Pharmacokinetic (PK) Analysis

In some embodiments, patients or subjects of the present disclosure may have blood samples taken for PK analysis during treatment with KXX, either alone, or co-administered with an immunosuppressive or immunomodulatory agent, such as MTX. Although limited PK results have been reported in subjects receiving pegloticase, and no PK studies have been performed in subjects weighing >120 kg, the present disclosure provides PK analysis in patients receiving KXX treatment, either alone or co-administered with an immunosuppressive agent or therapy. Sundy et al. (JAMA 306(7):711-20, 2011) reported results from 24 subjects with refractory gout who received single doses from 0.5 to 12 mg of pegloticase. PK parameters included plasma uricase activity (pUox) and the plasma urate concentration (pUAc). In this study, the pUox half-life was 6.4 to 13.8 days. After doses of 4 to 12 mg, the pUAc fell within 24 to 72 hours, from a mean±SD value of 11.1±0.6 mg/dL to 1.0±0.5 mg/dL; the AUC value for the pUAc was equivalent to maintaining the pUAc at 1.2 to 4.7 mg/dL for 21 days post-infusion. It remains uncertain whether body mass affects drug distribution. Since pegloticase is administered as a single dose regardless of body mass, this is important to assess.

Joint Imaging

In some embodiments, joint imaging may be performed for patients or subjects receiving KXX, either alone or co-administered with immunosuppressive therapy, such as MTX. Clinical research has shown that measuring tophus volume alone in gout is incomplete as successful therapy also needs to be associated with a reduction in inflammation, chronic synovitis, acute flares and slowing the progression or even healing of bone erosion, and thus, application of all-inclusive measurements that can measure all parameters of the physiologic impact of urate deposition will allow for comprehensive assessment of chronic gout and the impact of treatment. In some embodiments, a sub-study may also be performed to assess the ability of DECT and DCE-MRI to measure treatment response to pegloticase in subjects with chronic refractory gout.

Co-Administration of KXX and Immunosuppressive Therapy

Immunogenicity in response to pegloticase therapy (anti-pegloticase antibodies) may give rise to low serum drug levels, loss of therapeutic response, poor drug survival, and/or adverse events (e.g., IR). The development of anti-drug antibodies can be influenced by drug- and treatment-related factors, as well as participant characteristics. A potential prophylactic strategy to manage anti-drug antibody response with biologic response modifiers is the co-administration of immune modulating therapy. Reduction of immunogenicity with concomitant administration of other biologic agents (e.g., methotrexate use with adalimumab, infliximab) has been attributed to two mechanisms: 1) an immune modulating effect downregulating B cell activation, differentiation, and immunoglobulin production, and 2) alteration in Fc gamma R-mediated clearance mechanisms leading to prolongation of the half-life of monoclonal antibodies.

Thus, in some embodiments, the addition of immune modulating therapy (i.e., co-administration of KXX with an immunosuppressive or immunomodulatory agent) with an induction regimen or loading dose provides additive benefit in abrogating immunogenicity associated with biologics. As described herein, the immune modulating agent, methotrexate (MTX), is beneficial for use as a therapy to improve treatment efficacy and reduce IR in patients being treated for chronic gout with KXX, and to enhance the response rate seen with pegloticase alone in adults with uncontrolled gout.

Various embodiments of the disclosure provide for treatment of gout or gout related symptoms by administering KXX, either alone or co-administered with an immunosuppressive or immunomodulatory agent. In some embodiments, KXX may be administered alone to a patient for treatment of gout. In other embodiments, KXX may be co-administered with an immunosuppressant, such as MTX, for a combined immunosuppressive therapy. As used herein, “immunosuppressive agent” may also be referred to as “immunosuppressant” or “immunosuppressive therapy.” In some embodiments, an “immunosuppressant” may also be referred to herein as an “immunomodulatory agent.”

Administration of an immunosuppressive drug may reduce or eliminate any immune reactions that may occur in the patient. An immune reaction that may be encountered in a drug treatment as described herein may be an allergic reaction or any associated symptoms, including, but not limited to, hives, itching, nasal congestion, rash, scratchy throat, watery or itchy eyes. Severe allergic reactions may have additional symptoms, including, but not limited to abdominal cramping or pain, pain or tightness in the chest, intestinal upset, dizziness, nausea, weakness, or the like. In some embodiments, a severe allergic reaction may include symptoms of anaphylaxis as described herein. Drug reactions may be referred to herein as adverse events (AEs), and may be mild AEs or may be serious AEs (SAEs). Such combination of KXX and another drug, such as MTX, may reduce adverse events in a patient or subject. Thus, in some embodiments, administration of an immunosuppressive therapy with KXX may be beneficial for patients having gout or symptoms thereof. In some embodiments, a patient or subject may be an individual having a serum uric acid level of ≥6 mg/dL.

In some embodiments, co-administration of a PEGylated uricase as described herein and MTX results in normalization of the serum uric acid level in a patient relative to a patient not receiving co-administration of the PEGylated uricase and MTX. In some embodiments, the serum uric acid level may be reduced to less than 6 mg/dL as a result of co-administration of the PEGylated uricase and MTX. In other embodiments, the serum uric acid level may be reduced to less than 5 mg/dL as a result of co-administration of the PEGylated uricase and MTX. In another embodiment, the serum uric acid level is reduced to less than 2 mg/dL as a result of co-administration of the PEGylated uricase and MTX.

In some embodiments, patients or subjects weighing less than 120 kg may benefit from a particular dosage of KXX, or a particular dosage regiment, as described herein. For example, patients weighing less than 120 kg may be initially treated with a tolerizing dose of KXX, such as a dose of 8 mg KXX on a weekly basis for 3 weeks for a total of 3 doses. In some embodiments, such tolerizing dosage may be altered as deemed necessary by a clinician or practitioner.

Alternatively, for patients weighing greater than or equal to 120 kg, a tolerizing dose of KXX may include a dose of 8 mg, 12 mg, or 16 mg KXX intravenously at the first week of treatment for a total of one dose, followed by 8 mg intravenously on a weekly basis for 2 weeks after the first week of treatment, for a total of 2 doses. Such alternate dosing may be beneficial for patients having greater body weight, or a higher body mass index (BMI). In some embodiments, patients weighing greater than or equal to 120 kg may be grouped into treatment groups, with each group receiving a different tolerizing dosage of KXX. For example, one group may receive a tolerizing dose of 8 mg KXX, while another group may receive a tolerizing dose of 12 mg KXX, and still another group may receive a tolerizing dose of 16 mg KXX.

In some embodiments, KXX may be administered to a patient following a tolerizing dose at a dosage such as 8 mg by intravenous infusion every 2 weeks. This dosage may be continued for any period of time deemed appropriate by a clinician or practitioner. For example, 8 mg KXX may be given to a particular patient every 2 weeks following a tolerizing dosage regimen and lasting for a period of time totaling 2 weeks, 3 weeks, 4 weeks, 5 weeks, 6 weeks, 7 weeks, 8 weeks, 9 weeks, 10 weeks, 11 weeks, 12 weeks, 13 weeks, 14 weeks, 15 weeks, 16 weeks, 17 weeks, 18 weeks, 19 weeks, 20 weeks, 21 weeks, 22 weeks, 23 weeks, 24 weeks, 25 weeks, 26 weeks, 27 weeks, 28 weeks, 29 weeks, 30 weeks, 31 weeks, 32 weeks, 33 weeks, 34 weeks, 35 weeks, 36 weeks, 37 weeks, 38 weeks, 39 weeks, 40 weeks, 41 weeks, 42 weeks, 43 weeks, 44 weeks, 45 weeks, 46 weeks, 47 weeks, 48 weeks, 49 weeks, 50 weeks, 51 weeks, 52 weeks, 53 weeks, 54 weeks, 55 weeks, 60 weeks, 65 weeks, 70 weeks, or the like. In some embodiments, KXX may be given to a patient for more than 6 months, or more than 7 months, or more than 8 months, or more than 9 months, or more than 10 months, or more than 11 months, or more than 12 months, or more than 13 months, or more than 14 months, or more than 15 months, or more than 18 months, or more than 24 months. In other embodiments, KXX may be given to a patient for any length of time deemed appropriate by a clinician or practitioner, and as described herein, for the remainder of the patient's life.

In some embodiments, the patient may be treated with KXX plus an immunosuppressive or immunomodulatory agent or therapy for at least one month. In some embodiments, the patient is treated for 2 months, 3 months, 4 months, 5 months, 6 months, 7 months, 8 months, 9 months, 10 months, 11 months, 12 months, 13 months, 14 months, 15 months, 18 months, 21 months, 24 months, 30 months, 36 months, or more. In some embodiments, the patient may be treated for up to 52 weeks, or 51 weeks, or 50 weeks, or 49 weeks, or 48 weeks, or 47 weeks, or 46 weeks, or 45 weeks, or 44 weeks, or 43 weeks, or 42 weeks, or 41 weeks, or 40 weeks, or 39 weeks, or 38 weeks, or 37 weeks, or 36 weeks, or 35 weeks, or 34 weeks, or 33 weeks, or 32 weeks, or 31 weeks, or 30 weeks, or 25 weeks, or 20 weeks, or 17 weeks, or 12 weeks, or 6 weeks, or 4 weeks, or 2 weeks, or 24 months, or up to 36 months, or up to 48 months. In some embodiments, the patient may be treated for more than 24 months. In some embodiments, the patient is treated with for the rest of the patient's life.

In some embodiments, a tolerizing dosage regimen as described herein may be combined with the use or co-administration of an immunosuppressive agent or therapy. Such a tolerizing dosage regimen may involve escalation of a dose of KXX and an immunosuppressive agent or therapy such that the patient or subject is able to better tolerate KXX or the dosage thereof. In other embodiments, such a tolerizing dosage regimen may involve increasing or escalating doses of KXX with a particular dose of an immunosuppressive agent or therapy. Such treatments may be employed for any duration as described herein.

In some embodiments, treatment with KXX either alone or co-administered with an immunosuppressive or immunomodulatory agent, may be continued as appropriate for any length of time, as long as the patient experiences an improvement in the symptoms or signs of gout. Such signs/symptoms of gout that may serve as a metric for improvement in disease severity may include, but are not limited to, serum uric acid level, peripheral joint urate deposition volume, and inflammatory volume. For example, KXX treatment, either alone, or co-administered with an immunosuppressive agent, such as MTX, may be monitored with regular assessment of the patient or subject before, during, and following treatment. Any number of diagnostic or evaluative testing procedures may be performed at any time, and at any frequency as deemed necessary by a clinician or practitioner.

KXX treatment typically is monitored using regular determination of the patient's SUA levels. A reduction in the serum uric acid level relative to the SUA in the patient before KXX treatment may generally be indicative of successful treatment with KXX, alone, or co-administered with an immunosuppressive agent or therapy, such as MTX, as described herein. Collection and measurement of a patient's serum uric acid levels are known to those of skill in the art. In some embodiments, the patient's serum uric acid levels are assayed before each KXX therapy. In some embodiments, any suitable method for collecting appropriate samples and methods of measuring or quantifying uric acid levels may be used in accordance with the disclosure.

Additional measurements to assess the efficacy and safety of KXX treatment may be used in accordance with the disclosure. These may include trough KXX levels, anti-KXX antibody levels, and/or anti-PEG antibody levels. In some embodiments, these measurements may be taken prior to each dose of KXX after the first dose. In other words, an initial dose of KXX may be administered to a patient without measurement of KXX levels, anti-KXX antibody levels, and/or anti-PEG antibody levels. Then, prior to each subsequent dose of KXX, such measurements may be taken as described herein. For treatment regiments wherein KXX is co-administered with an immunosuppressive agent or therapy, the same measurements may be taken at the same time periods, without deviating from the scope of the disclosure. Such measurements may be obtained from each patient as necessary to evaluate response to the treatment, or a lack thereof. Specific criteria for responders and non-responders to treatment with KXX are described in the Examples.

For example, in some embodiments, serum uric acid levels may be evaluated to assess the response rate of the patient to the KXX+MTX therapy or treatment. Some embodiments provide for lowering or normalization of the SUA levels to 6 mg/dL or below as described herein. Other embodiments provide for lowering or normalization of the SUA levels to 5 mg/dL or below as described herein. In some embodiments, certain objectives of the present disclosure and the studies described herein may include estimation of response rate during Month 3 (i.e., Weeks 10, 12 and 14) of KXX+MTX therapy, as measured by the sustained normalization of SUA to <6 mg/dL for at least 80% of the time during Month 3 in subjects receiving pegloticase with MTX. In some embodiments, estimation may be performed of the overall response rate, as measured by the sustained normalization of SUA to <6 mg/dL for at least 80% of the time during both Month 3 (Weeks 10, 12 and 14) and Month 6 (Weeks 20, 22 and 24) combined of KXX+MTX therapy in subjects receiving pegloticase with MTX. In other embodiments, estimation may be performed of the 5 mg/dL response rate during Month 3, during Month 6, and Overall (Months 3 and 6 combined), as measured by the sustained normalization of SUA to <5 mg/dL for at least 80% of the time in subjects receiving pegloticase with MTX. In some embodiments, estimation may be performed of the mean change from baseline to Weeks 14, 24, 36, and 52 in SUA for subjects receiving KXX+MTX. Such measurements and the methods for their collection and evaluation are described in detail in the Examples.

In some embodiments, when KXX is co-administered with an immunosuppressive agent or therapy, such as MTX, additional measurements for assessing the efficacy of treatment may be obtained. For example, trough methotrexate metabolite levels may be obtained for each patient or subject prior to each dose of KXX, as described herein. In other embodiments, measurement of hematology and liver function may be obtained for each patient on a weekly basis during treatment. This type of measurement may provide information to clinicians relating to the breakdown of the immunosuppressive agent in the patient's body.

In some embodiments, co-administration of KXX and methotrexate immunosuppressive therapy results in normalization of the serum uric acid level in the patient relative to a patient not receiving KXX and MTX immunosuppressive therapy. As used herein, “normalization” refers to lowering of the serum uric acid level similar to that found in normal healthy patients. In other embodiments, normalization may refer to SUA levels being reduced to levels similar to that found in patients not requiring KXX treatment or therapy. In some embodiments, the serum uric acid level is normalized after KXX and methotrexate immunosuppressive therapy begins.

In some embodiments, as described herein, the serum uric acid level in patients treated with KXX and an immunosuppressive therapy such as MTX is reduced to less than 6 mg/dL as a result of treatment, including, but not limited to, 6 mg/dL, 5.9 mg/dL, 5.8 mg/dL, 5.7 mg/dL, 5.6 mg/dL, 5.5 mg/dL, 5.4 mg/dL, 5.3 mg/dL, 5.2 mg/dL, 5.1 mg/dL, 5 mg/dL, 4.9 mg/dL, 4.8 mg/dL, 4.7 mg/dL, 4.6 mg/dL, 4.5 mg/dL, 4.4 mg/dL, 4.3 mg/dL, 4.2 mg/dL, 4.1 mg/dL, 4 mg/dL, 3.9 mg/dL, 3.8 mg/dL, 3.7 mg/dL, 3.6 mg/dL, 3.5 mg/dL, 3.4 mg/dL, 3.3 mg/dL, 3.2 mg/dL, 3.1 mg/dL, 3 mg/dL, 2.9 mg/dL, 2.8 mg/dL, 2.7 mg/dL, 2.6 mg/dL, 2.5 mg/dL, 2.4 mg/dL, 2.3 mg/dL, 2.2 mg/dL, 2.1 mg/dL, 2 mg/dL, 1.9 mg/dL, 1.8. mg/dL, 1.7 mg/dL, 1.6 mg/dL, 1.5 mg/dL, 1.4 mg/dL, 1.3 mg/dL, 1.2 mg/dL, 1.1 mg/dL, 1 mg/dL, or the like. In other embodiments, the serum uric acid level may be reduced to less than 5 mg/dL as a result of treatment. In still further embodiments, the serum uric acid level is reduced to less than 2 mg/dL as a result of KXX and methotrexate immunosuppressive therapy. Treatment with KXX plus an immunosuppressive therapy may be able to reduce the serum uric acid levels to levels that result in improvement of symptoms associated with gout as described herein.

In some embodiments, normalization of the SUA levels in a subject may be achieved within a specific amount of time as a measurement of success or efficacy. For example, in some embodiments, normalization of the SUA may be achieved by 2 weeks after initiation of treatment with KXX+MTX, such as by week 1, or week 2, or week 3, or week 4, or week 5, or week 6, or week 7, or week 8, or week 9, week 10, or week 11, or week 12, or week 13, or week 14, or week 15, week 16, or week 17, or week 18, or week 19, or week 20, or week 21, or week 22, or week 23, or week 24, or week 25, or week 26, or week 27, or week 28, or week 29, or week 30, or week 31, or week 32, or week 33, or week 34, or week 35, or week 36, or week 37, or week 38, or week 39, or week 40, or week 41, or week 42, or week 43, or week 44, or week 45, or week 46, or week 47, or week 48, or week 49, or week 50, or week 51, or week 52, or week 53, or week 54, or week 55, or week 56, or week 57, or week 58, or week 59, or week 60, or the like.

In some embodiments, treatment of a patient or subject with KXX plus an immunosuppressive or immunomodulatory agent such as MTX results in a reduction of the incidence of infusion reaction, gout flare, or anaphylaxis.

In some embodiments, the level of MTX metabolite is increased relative to a patient not receiving KXX and methotrexate immunosuppressive therapy.

In some embodiments, analysis of the efficacy of a method as described herein for treating gout may further comprise measurements to assess disease severity. For example, a diagnostic imaging test, such as including, but not limited to, computed tomography (CT), magnetic resonance imaging (MRI), X-ray, ultrasound, positron emission tomography (PET), fluoroscopy, or the like.

In some embodiments, peripheral joint urate deposition volume and inflammatory volume may be measured in a patient and used to evaluate disease severity or to evaluate efficacy of the drug treatment. For example, in some embodiments, peripheral joint urate deposition volume is reduced in the patient relative to a patient not receiving KXX and methotrexate immunosuppressive therapy. In other embodiments, peripheral joint urate deposition volume is determined by dual-energy computed tomography (DECT) scanning. In other embodiments, inflammatory volume is reduced in the patient relative to a patient not receiving KXX and methotrexate immunosuppressive therapy. In other embodiments, inflammatory volume is determined by Dynamic Contrast Enhanced—Magnetic Resonance Imaging (DCE-MRI) or MRI without contrast, or both.

In some embodiments, administration of KXX alone or co-administration of KXX with an immunosuppressive therapy or agent or with a drug having monomethoxypoly(ethylene glycol) (PEG) may elicit an immune reaction in the patient or subject. Evaluation of antibodies in a subject or patient receiving KXX therapy may provide an assessment of such an immune reaction to the drug treatment. For example, in some embodiments, determination of a mean titer of anti-KXX antibodies or anti-monomethoxypoly(ethylene glycol) (PEG) antibodies may be performed to determine an immune reaction in the patient or subject, or to determine the efficacy of immunosuppressive therapy. In some embodiments, a mean titer of anti-KXX antibodies may be determined for a patient. In other embodiments, a mean titer of anti-monomethoxypoly(ethylene glycol) (PEG) antibodies may be determined. In some embodiments, antibody titers may be any value determined by any appropriate measurements or analyses. Antibody titers in a patient as used herein are a metric for and may indicate an immune response to a drug such as KXX. In some embodiments, an antibody titer as described herein may refer to antibodies in a patient directed against KXX or PEG. In some embodiments, an anti-KXX or anti-PEG mean antibody titer may be less than or equal to about 1:6000 as a result of KXX administration. For example, an antibody titer for a patient receiving KXX therapy, either alone or in combination with MTX, may be less than or equal to about 1:100, about 1:200, about 1:300, about 1:400, about 1:500, about 1:600, about 1:700, about 1:800, about 1:900, about 1:1000, about 1:2000, about 1:3000, about 1:4000, about 1:5000, about 1:6000, about 1:7000, about 1:8000, about 1:9000, about 1:10000, or the like. In some embodiments, a responder may have an anti-KXX antibody titer of about 1:837±1687, or about 1:4211, or about 1:5898. In other embodiments, the antibody titers recited above may generally be found in patients who exhibit a positive response to KXX therapy (i.e., a responder). In some embodiments, a non-responder may have substantially or significantly higher antibody titers, for example, less than or equal to about 1:30000, about 1:40000, about 1:50000, about 1:60000, about 1:70000, about 1:80000, about 1:90000, about 1:100000, about 1:150000, about 1:200000, about 1:250000, about 1:300000, about 1:350000, about 1:400000, about 1:450000, about 1:500000, or the like. In some embodiments, a non-responder may have an anti-KXX antibody titer of about 1:34528±42,228. In other embodiments, such antibody titers may be determined for KXX treatment alone or may be determined for KXX+MTX immunosuppressive therapy. Anti-KXX or anti-PEG mean antibody titers as a result of KXX and MTX immunosuppressive therapy may be beneficially maintained at or below any threshold value tolerable for the patient.

In some embodiments, anti-drug antibody titers may be reduced as a result of use of an immunosuppressive agent or therapy, such as MTX as described herein. In other embodiments, the titer of specific types of antibodies may be reduced. For example, in some embodiments, the levels or titer of any specific type of antibodies may be reduced as a result of KXX co-administered with an immunosuppressive agent or therapy, such as IgG antibodies, IgA antibodies, IgM antibodies, IgD antibodies, IgE antibodies, or combinations thereof.

In some embodiments, evaluation of antibody titers may be beneficial for patients receiving KXX, either alone, or co-administered with an immunosuppressive agent or therapy such as MTX, for the first time. In other embodiments, evaluation of antibody titers may be beneficial for patients who have developed anti-KXX antibodies, or who have been classified as non-responders to KXX treatment. Criteria for classifying a patient or subject as a responder or a non-responder are described herein elsewhere.

In some embodiments, heavier and/or younger patients may have a higher incidence of anti-KXX antibodies, or may have higher anti-KXX drug titers, than lighter and/or older patients. In other embodiments, lighter and/or older patients may have higher drug loading of KXX than heavier and/or younger patients. In some embodiments, lighter patients may have higher exposures of KXX than heavier patients. For example, in some embodiments, lighter patients may have greater than 2-fold exposure to KXX than heavier patients. In some embodiments, lower drug levels in a patient may result in anti-KXX antibodies. For example, the mean area under the curve (AUC) for lighter patients may be about 8.92 mg/L versus about 4.04 mg/L in heavier patients. In other embodiments, older patients may have higher exposures of KXX than younger patients. For example, in some embodiments, older patients may have greater than 2-fold exposure to KXX than younger patients. In some embodiments, the mean area AUC for older patients may be about 8.86 mg/L versus about 3.93 mg/L in younger patients, indicating that younger patients may have a more robust immune system. Thus, in some embodiments, additional 8-mg doses of KXX may be beneficial for younger and/or heavier patients. In other embodiments, younger and/or heavier patients may benefit from one or more loading doses of 16 mg of KXX.

In some embodiments, production of anti-drug antibodies, such as antibodies to KXX, may be reduced or eliminated by increasing the amount of KXX delivered to a patient, i.e., maintaining higher trough levels of KXX in a patient. Higher trough levels of KXX may reduce anti-drug antibody production. In some embodiments, possible dosing strategies for increasing the amount of KXX delivered to a patient, and thus producing higher trough levels in the patient, may include reducing the interval between doses of KXX, or using higher doses at the beginning of and/or during treatment. Another possible strategy for reducing anti-KXX antibodies is the use of immunomodulators, such as MTX, as described herein. Immunomodulators may reduce or eliminate an immune response to unfamiliar proteins. One of skill in the art will understand that other immunomodulators may be used with similar results, including, but not limited to, corticosteroids (i.e., prednisone), Rapimmune, myophenolate, methotrexate, or the like.

The methods disclosed herein presume that the patient is effectively receiving all the prescribed dose. In some embodiments, depending on the age of the patient, it may be difficult to deliver a drug to a patient, for example when administering a drug to an infant and, therefore, the compliance and effectiveness of drug delivery by the patient's parent(s), guardian(s), or health care provider(s) may also be assessed.

Definitions

Where a range of values is provided, it is understood that each intervening value, to the tenth of the unit of the lower limit unless the context clearly dictates otherwise, between the upper and lower limit of that range and any other stated or intervening value in that stated range, is encompassed within the disclosure. The upper and lower limits of these smaller ranges may independently be included in the smaller ranges, and are also encompassed within the disclosure, subject to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included in the disclosure.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. Although any methods and materials similar or equivalent to those described herein can also be used in the practice or testing of the present disclosure, the preferred methods and materials are now described. All publications mentioned herein are incorporated herein by reference to disclose and describe the methods and/or materials in connection with which the publications are cited. The publications discussed herein are provided solely for their disclosure prior to the filing date of the present application. Nothing herein is to be construed as an admission that the present disclosure is not entitled to antedate such publication by virtue of prior disclosure. Further, the dates of publication provided may be different from the actual publication dates which may need to be independently confirmed.

As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, “an active agent” refers not only to a single active agent but also to a combination of two or more different active agents, “a dosage form” refers to a combination of dosage forms as well as to a single dosage form, and the like.

Unless defined otherwise, all technical and scientific terms used herein have the meaning commonly understood by one of ordinary skill in the art to which the disclosure pertains. Specific terminology of importance to the description of the present disclosure is defined below.

As used herein “KXX” may be used interchangeably with KRYSTEXXA® or pegloticase. Likewise, as used herein, “Pegloticase+IMM Period” may also be referred to herein as “KXX+IMM Period.”

“IMM” as used herein refers to an immunomodulatory agent, such as MTX as described herein. As such, IMM may also be used interchangeably herein with MTX. Therefore, “Pegloticase+IMM Period” or other similar terminology refers to the presently described co-administration or concomitant administration of KXX and MTX.

As used herein, an “adverse event” or “AE” refers to any untoward medical occurrence associated with the use of a drug in humans, whether it is considered drug-related or not. An AE or suspected adverse reaction is considered a “serious adverse event” or “SAE” if, in the view of either the Investigator or Sponsor, it results in any of the following outcomes: (1) Death, (2) Life-threatening: an AE is considered “life-threatening” if, in the view of either the Investigator or Sponsor, its occurrence places the subject or subject at immediate risk of death. It does not include an AE that, had it occurred in a more severe form, might have caused death; (3) Inpatient hospitalization or prolongation of existing hospitalization; (4) A persistent or significant incapacity or substantial disruption of the ability to conduct normal life functions. (5) A congenital anomaly/birth defect; (6) Important medical events that may not result in death, be life-threatening, or require hospitalization may be considered serious when, based upon appropriate medical judgment, they may jeopardize the patient or subject and may require medical or surgical intervention to prevent one of the outcomes listed in this definition. Examples of such medical events include allergic bronchospasm requiring intensive treatment in an emergency room or at home, blood dyscrasias or convulsions that do not result in inpatient hospitalization, or the development of drug dependency or drug abuse.

As used herein, “anaphylaxis” refers to a severe, acute onset allergic reaction that may occur over minutes to several hours. Anaphylaxis may involve the skin, mucosal tissue, or both, and may have one or more symptoms including, but not limited to, generalized hives, pruritus (itching), flushing, swelling of the lips, tongue, throat or uvula, shortness of breath, vomiting, lightheadedness, wheezing, hemodynamic instability, and rash or urticaria. In addition, anaphylaxis may be accompanied by at least one of the following: respiratory compromise (e.g., dyspnea, wheeze-bronchospasm, stridor, reduced peak expiratory flow, hypoxemia), and reduced blood pressure (i.e., systolic blood pressure <90 mm Hg or greater than 30% decrease from that person's baseline) or associated symptoms of end-organ failure (e.g., hypotonia [collapse], syncope, incontinence). Anaphylaxis in accordance with the disclosure is defined by the National Institute of Allergy and Infectious Disease/Food Allergy and Anaphylaxis Network (NIAID/FAAN) clinical criteria for diagnosing anaphylaxis. Anaphylaxis reactions were reported as a serious adverse event (SAE) for the present disclosure.

Cardiovascular Events: The following cardiovascular events were collected. Major Adverse Cardiovascular Events (MACE) defined as: Non-Fatal Myocardial Infarction: The presence of at least 2 of the 3 following criteria: 1) chest pain consistent with angina, 2) abnormal values of cardiac enzymes (>upper limit of normal of the MB fraction of creatinine phosphokinase and/or troponin that follows a pattern of myocardial injury), 3) myocardial injury current (ST segment elevation) or the development of new Q waves in 2 contiguous leads of the electrocardiogram. Non-Fatal Stroke: ischemic or hemorrhagic stroke defined as an acute, focal neurologic event that persisted for >24 hours. If neurologic symptoms last for <24 hours but magnetic resonance imaging (MRI) confirms an infarct, it was considered as a stroke. Confirmation by imaging studies (magnetic resonance imaging or computerized tomography of the brain) were sought in all cases but was not an absolute requirement for consideration of the event. Cardiovascular deaths: including any death from a cardiovascular cause including: myocardial infarction, stroke, heart failure, arrhythmic death, aortic dissection or rupture, any fatal thromboembolic event, sudden cardiac death, any death of unknown cause and unwitnessed death. Congestive heart failure defined as: hospitalization or prolonged (>12 hours) emergency department visit due to dyspnea, shortness of breath, with progressive edema accompanied by clinical findings of pulmonary vascular congestion. Radiographic and/or echocardiographic documentation is desirable but not required. Treatment by intravenous (Parenteral) diuretics or inotropes is required to confirm this diagnosis versus ultrafiltration, hemodialysis or left ventricular assist devices.

Clinical Laboratory Safety Tests: For the open-label study, blood (for hematology and clinical chemistry) and urine (for uric acid:creatinine ratio) samples were collected at the Screening, Week −4 (prior to the first dose of MTX), and Week −2 Visits during the Screening/MTX Run-in Period; prior to pegloticase infusion on Day 1 and at the Weeks 2, 6, 14, 22, 24 and 36, Visits during the Pegloticase+IMM Period; and the non-infusion End of Pegloticase Infusions Visit (if applicable), Week 52/End of Study/Early Termination and 3 and 6 month Post Treatment Follow-up Visits. For the randomized study, Blood (for hematology and clinical chemistry) was collected at the Screening, Week -6 (prior to the first dose of MTX), and Week −4 and −2 Visits during the Run-in Period; prior to pegloticase infusion on Day 1 and at the Weeks 2, 6, 14, 22, 24, 36 and the non-infusion End of Pegloticase Infusions Visit (if applicable), Week 52/End of Study/Early Termination and 3 and 6 month Post Treatment Follow-up Visits.

Urine (for albumin:creatinine ratio and allantoin acid) samples were collected prior to the pegloticase infusion on Day 1 and at the Weeks 14, 24, 36 and the non-infusion End of Pegloticase Infusions Visit (if applicable) and Week 52/End of Study/Early Termination Visits.

Urine (for human chorionic gonadotropin) samples were collected at all visits except the Screening Visit and Weeks 21, 23 and 3- and 6-month Post Treatment Follow-up Visits for all female subjects of childbearing potential.

Safety laboratory assessments may include: Hematology: complete blood count with differential (hemoglobin concentration, hematocrit, erythrocyte count, platelet count, leukocyte count, and differential leukocyte count); Chemistry: albumin, transaminases (aspartate aminotransferase, alanine aminotransferase), alkaline phosphatase, total bilirubin, creatinine (including calculation for eGFR calculated by the abbreviated MDRD equation : creatinine (including calculation for eGFR calculated by the MDRD study equation : 175×(Scr[mg/dL])⁻1.154× (age)^(−0.203)× (0.742 if female)×(1.212 if African American) or 175×(S_(cr)[μmol/L]/88.4)⁻1.154× (age)^(−0.203)× (0.742 if female)×(1.212 if African American), glucose, sodium, potassium, calcium, chloride, total protein, blood urea nitrogen, and human chorionic gonadotropin (at the Screening Visit for all female subjects of childbearing potential); Urine: uric acid:creatinine ratio and human chorionic gonadotropin (at all visits except the Screening Visit for all female subjects of childbearing potential).

As used herein, “co-administration” refers to the simultaneous administration of one or more drugs with another in a treatment regimen. For example, as described herein, co-administration of KXX with MTX may refer to administration of MTX at the same time as KXX or may refer to administration of MTX at a specific period of time before or after KXX administration. In some embodiments, MTX may be administered before KXX. In other embodiments, KXX may be administered before MTX. In other embodiments, both drugs are administered at the same time. As described herein elsewhere, co-administration may also refer to any particular time period of administration of either KXX or MTX, or both. For example, as described herein, MTX may be administered hours, days, weeks, or months before KXX treatment, as long as both drugs are to be provided to a patient or subject in a particular treatment regimen. In other embodiments, MTX may be administered to a patient hours, days, weeks, or months after KXX treatment. In some embodiments, co-administration may refer to any time of administration of KXX and/or MTX such that both drugs are present in the body of a patient at the same. In some embodiments, either drug may be administered before or after the other, so long as they are both present within the patient for enough time that the patient received the intended clinical or pharmacological benefits.

As used herein, “concomitant administration” refers to a therapeutic or drug regimen in which one or more medications are given together, i.e., at the same time. In some embodiments, concomitant administration and co-administration may be referred to interchangeably.

Digital Photography: Digital photography of the hands and feet was completed at Week -6, Day 1 and Weeks 14, 24, 36, and the End of Pegloticase Infusions Visit (if applicable) and Week 52/End of Study/Early Termination and the 3- and 6-month Post Treatment Follow-up Visits for the randomized study. Other anatomical sites with large tophi may be photographed in addition to the hands and feet at the Investigator's discretion.

Dual-energy Computed Tomography (DECT): For sites with DECT capability, DECT was obtained at Day 1 and Weeks 24, 36 Visits, or at Day 1 and weeks 14, 24, visits during the Pegloticase+IMM Period for the open-label and randomized studies, respectively; at the End of Pegloticase Infusions Visit (if applicable), the Week 52/End of Study/Early Termination Visit during the and 52/End of Study/Early Termination. The DECT may be completed within+/−5 days of the scheduled timepoint. Subjects who end pegloticase infusions prior to Week 52 followed the scheduled timepoints but avoid a repeat DECT scan within 6 weeks of a prior scan. Images were obtained for the hands/wrists, knees, ankles/feet, and the Investigator identified the primary area of major urate deposition. The imaging was performed by a study-specific, qualified radiologist.

Electrocardiogram: A 12-lead ECG was performed on Day 1 before the pegloticase infusion for all subjects and at the discretion of the Investigator thereafter.

By the terms “effective amount” and “therapeutically effective amount” of an agent, compound, drug, composition or combination which is nontoxic and effective for producing some desired therapeutic effect upon administration to a subject or patient (e.g., a human subject or patient).

As used herein, a “gout flare” refers to a manifestation of physiological or biochemical symptoms of gout, which is a possible side effect or AE associated with treatment with KXX. A gout flare may produce burning itching, tingling, or stiffness in the joints, particularly the peripheral joints. An individual may also experience redness, swelling, and pain in the joints. In accordance with the disclosure, gout flares may initially increase when starting treatment with KXX. For such individuals, medications to help reduce flares may be taken regularly for the first few months after KXX is started. Prophylactic treatment for gout flares may include, but is not limited to, colchicine or non-steroidal anti-inflammatory drugs (NSAID). In some embodiments, prophylactic treatment may be given prior to an infusion of KXX, for example one week prior to treatment with KXX.

As used herein, “glucose-6-phosphate dehydrogenase (G6PD) Deficiency” or “G6PD” refers to a condition caused by an inborn error of metabolism that predisposes an individual to red blood cell breakdown. Individuals with G6PD deficiency are not included in the present study and are generally advised not to take KXX.

As used herein, “immuno-tolerance” refers to the lack of an immune response in a patient as a result of a drug treatment such as KXX. In some embodiments, establishing immune-tolerance may also refer to reducing immunogenicity to KXX, or to reduce or prevent loss of a response to KXX. Such loss of response may be the result of the formation of anti-drug antibodies, which may increase clearance of KXX, causing a loss of response.

Individual Tophi Response: All measurable tophi were measured bi-dimensionally (using the longest diameter and the longest perpendicular to that diameter) and the response of each individual tophus was categorized according to the change from baseline in area of each tophus at each visit as follows: Complete Response (CR)—A 100% decrease in the area of the tophus; Marked Response (MR)—At least a 75% decrease in the area of the tophus; Stable Disease (SD)—Neither a 50% decrease nor a 25% increase in the area of the tophus can be demonstrated; Progressive Disease (PD)—A 25% or more increase in the area of the tophus; Unable to Evaluate (UE)—The tophus cannot be accurately measured for any reason at any given post-baseline time point (e.g., image missing or of poor quality, obvious infection of the tophus).

Each individual unmeasured tophus was semi-quantitatively assessed based upon the impression of the central reader using the following guideline: Complete Response—the disappearance of the tophus; Improved—an approximate 50% or more reduction from baseline in the size of the tophus; Stable Disease—neither improvement nor progression from baseline can be determined; Progressive Disease—an approximate 50% or more increase from baseline in the area of the tophus. Unable to Evaluate—the tophus cannot be assessed for any reason at any given post-baseline time point (e.g., image missing or of poor quality, or obvious infection of the tophus).

The overall response for a subject was based upon the best response among all tophi (including measurable and unmeasured) for that subject (e.g., if any one tophus shows complete response, the overall response is Complete Response). If any single tophus shows progression, or if a new tophus appears during the study, the overall response for that subject was Progressive Disease, regardless of the response of any other tophi. New tophi arising outside of the regions photographed at baseline were captured by the Investigator on the case report form, and also resulted in an overall response assessment of Progressive Disease.

As used herein, an “infusion reaction” or “IR” refers to a reaction of a patient or subject to a drug. Infusion reactions generally refer to drugs administered by intravenous (IV) infusion. most common signs and symptoms of an infusion reaction, including urticaria (skin rash), erythema (redness of the skin), dyspnea (difficulty breathing), flushing, chest discomfort, chest pain, and rash. For the present disclosure, IRs were recorded as Infusion Reaction AEs. If the IR meets the definition for “Serious” as described herein, it is also reported as an SAE. In some embodiments, an IR was defined as any infusion-related AE or cluster of temporally-related AEs, not attributable to another cause, which occur during or within 2 hours after the infusion of pegloticase. Other AEs that occur outside of the 2-hour window following the infusion may also be categorized as an IR per the discretion of each study site. Signs and symptoms of the IR, and treatments administered, were documented in the medical record and in the CRF. Examples of AEs not considered possible IRs include but are not limited to: laboratory abnormalities that are unlikely to have occurred during or within 2 hours following the infusion (e.g., anemia, hypercholesterolemia), gout flares, most infectious diseases, or the recurrence or worsening of a known chronic medical problem identified in the participant's medical history.

As used herein, “IR Prophylaxis” refers to a treatment regimen to prevent infusion reactions. In some embodiments, all participants received pre-treatment prophylaxis consisting of at least an antihistamine and corticosteroid prior to each infusion of pegloticase. In some embodiments, to standardize this prophylaxis regimen, participants may take (60 mg) fexofenadine orally the night before and again on the morning of the infusion with 1000 mg/day of acetaminophen. Prior to the infusion, hydrocortisone 200 mg IV was administered and a targeted physical exam was performed. The name, dose, route, date, and time of administration of each prophylactic medication were recorded in the medical record and in the CRF.

Joint Pain Assessment: Joint pain was assessed at the Screening and Week −4 (prior to the first dose of MTX) Visits during the MTX Run-in Period; prior to pegloticase infusion at the Day 1 and Weeks 14, 24 and 36 Visits during the Pegloticase+IMM Period; at the End of Pegloticase Infusions Visit (if applicable); the Week 52/End of Study/Early Termination Visit and the Post Treatment Periods 3 and 6 Month Follow-up Visits.

As used herein, “KRYSTEXXA®” or “KXX” or “pegloticase” or “PEGylated uricase” refers to a covalent conjugate of uricase produced by a genetically modified strain of Escherichia coli and monomethoxypoly (ethylene glycol). Although the term “uricase” or “PEGylated uricase” may be used herein to refer to a PEGylated uricase such as KRYSTEXXA®, one of skill in the art would understand that many different forms of a uricase may be known and used in accordance with the disclosure, and therefore any PEGylated uricase, such as KRYSTEXA or KXX, may be used for treatment of a patient with elevated SUA as described herein.

As used herein, the term “normal uric acid level” refers to a patient's blood plasma uric acid concentration in a range that does not cause physiological or biochemical symptoms or signs of gout. In some embodiments, a normal uric acid level may not exceed the biochemical limit of solubility. For females, a normal uric acid range may fall between about 2.4 mg/dL and about 6 mg dL, and for males, about 3.4 mg/dL to about 7 mg/dL. One of skill in the art will recognize that these values may vary slightly depending on the subject or patient, as well as on the laboratory. As used herein, the term “elevated uric acid levels” refers to refers to a patient's blood plasma or serum uric acid concentration equal to or greater than about 6 mg/dL. In some embodiments, the uric acid level in a patient may be normalized to less than about 6 mg/dL, or less than about 5 mg/dL, or less than about 2 mg/dL, following treatment with KXX, either alone or co-administered with an immunosuppressive agent or therapy. To this effect, uric acid levels can vary based on the particular testing methodology and from laboratory to laboratory.

Patient Global Assessment: The patient global assessment was collected at the Screening and Week −4 (prior to the first dose of MTX) Visits during the MTX Run-in Period; prior to KXX infusion at the Day 1 and Weeks 14, 24 and 36 Visits during the KXX+MTX Period; at the End of Pegloticase Infusions Visit (if applicable); the Week 52/End of Study/Early Termination Visit and the Post Treatment Periods 3 and 6 Month Follow-up Visits.

By “pharmaceutically acceptable” is meant a material that is not biologically or otherwise undesirable, i.e., the material may be incorporated into a pharmaceutical composition administered to a patient without causing any undesirable biological effects or interacting in a deleterious manner with any of the other components of the composition in which it is contained. When the term “pharmaceutically acceptable” is used to refer to a pharmaceutical carrier or excipient, it is implied that the carrier or excipient has met the required standards of toxicological and manufacturing testing or that it is included on the Inactive Ingredient Guide prepared by the U.S. Food and Drug administration. “Pharmacologically active” (or simply “active”) as in a “pharmacologically active” (or “active”) derivative or analog, refers to a derivative or analog having the same type of pharmacological activity as the parent compound and approximately equivalent in degree. The term “pharmaceutically acceptable salts” include acid addition salts which are formed with inorganic acids such as, for example, hydrochloric or phosphoric acids, or such organic acids as acetic, oxalic, tartaric, mandelic, and the like. Salts formed with the free carboxyl groups can also be derived from inorganic bases such as, for example, sodium, potassium, ammonium, calcium, or ferric hydroxides, and such organic bases as isopropylamine, trimethylamine, histidine, procaine and the like.

Pharmacokinetic and Anti-drug Antibody Measurements: Serum samples for PK analysis of pegloticase were collected prior to the pegloticase infusion and after the end of infusion (prior to discharge) on Day 1 and at the Weeks 2, 4, 6, 8 and 36 Visits or weeks 2, 6, 14, 24, 36, for the open-label and randomized studies, respectively, and prior to the pegloticase infusion only at the Weeks 10, 14, 18, 22, 24 (open-label study); at the End of Pegloticase Infusions Visit (if applicable); and the Week 52/End of Study/Early Termination Visits. Visits for frequent sampling of a subset of subjects who consent for additional non-infusion visit PK sampling occured at Weeks 1 and 7 or at week 21 for the open-label and randomized studies, respectively.

Immunogenicity of pegloticase was assessed via serum samples for evaluation of anti-PEG and anti-uricase IgG antibodies. Samples were collected prior to the pegloticase infusion on Day 1 and at the Weeks 2, 4, 6, 8, 10, 14, 18, 22, 24, 36, or weeks 2, 6, 14, 22, 24, 36 for the open-label and randomized studies, respectively; at the End of Pegloticase Infusions Visit (if applicable); and 52/End of Study/Early Termination Visits and Post Treatment 3 month Follow-up Visit. Visits for frequent sampling of a subset of subjects who consent for additional non-infusion visit PK sampling occurred at Weeks 1 and 7 (open-label study). In the event of an AE suspected to be an infusion reaction, a serum sample was collected at that time or at the subsequent visit for evaluation of pegloticase antibodies.

Blood samples were collected prior to pegloticase infusion on Day 1 and at the Weeks 4, 8, 22 and 36 Visits or at Day 1 and weeks 14, 24, and 36 visits during the Pegloticase+IMM for MTX Polyglutamate analysis for the open-label and randomized studies, respectively.

For the randomized study, optional blood samples for PBMC, RNA isolation and serum were collected from each consenting subject prior to the first dose of MTX at Week −6, prior to the infusion on Day 1 and Weeks, 6, 14, 24, 36 and the End of Pegloticase Infusions Visit (if applicable) and the Week 52/End-of-Study/Early Termination. During visits at Weeks 2, 4, 8, 10 and 12, optional samples were only collected if subjects were experiencing an acute gout flare on the day of visit.

Subjects may still participate in the study even if they decline to provide consent for the optional future use blood samples.

Samples were retained for potential future analyses which may include biomarkers relevant to gout (e.g., inflammatory markers) or gout co-morbidities in response to pegloticase or other potential treatments for gout.

Physical Examinations: A complete physical examination was performed at the Screening Visit, including assessment of HEENT, heart, lungs, abdomen, skin, extremities, and neurological status, and/or musculoskeletal. The exam included assessment for presence of tophi, as well as gout history and symptom severity. For the open-label study, a targeted physical examination per the investigator judgement but at a minimum included heart, lungs and abdominal exam and include a joint and skin evaluation and assessment of AEs at Week −4, Day 1, and prior to administration of pegloticase at Weeks 4, 8, 12, 16, 20, 24, 36, the End of Pegloticase Infusions Visit (if applicable), Week 52/End of Study/Early Termination and 3 and 6 month Post Treatment Follow-up Visits. For the randomized study, a targeted physical examination per investigator judgement was conducted at Week −6, Day 1, and prior to administration of pegloticase at Weeks 4, 8, 12, 16, 20, 24, 36 and the non-infusion End of Pegloticase Infusions Visit (if applicable), Week 52/End of Study/Early Termination and 3 and 6 month Post Treatment Follow-up Visits; at a minimum this included heart, lungs, and abdominal exam.

Physician Global Assessment: The physician global assessment was collected at the Screening and Week −4 or week −6 (prior to the first dose of MTX) Visits during the MTX Run-in Period for the open-label and randomized studies, respectively; prior to pegloticase infusion at the Day 1 and Weeks 14, 24 and 36 Visits, and the Day 1 and week 6, 14, 20, 24, 30, 36, and 44 visits during the Pegloticase+IMM Period for the open-label and randomized studies, respectively; at the End of Pegloticase Infusions Visit (if applicable), the Week 52/End of Study/Early Termination Visit and the Post Treatment Periods 3 and 6 Month Follow-up Visits (open-label study).

As used herein, “prolonging” refers to extending the duration of the treatment effects of KXX therapy, either alone or co-administered with MTX. For example, as described herein, treatment of a patient with KXX co-administered with MTX, may result in a more enhanced response to the drug in the patient, resulting in a lowered SUA, when compared with treatment with KXX alone.

As used herein, “reducing” refers to a lowering or lessening, such as reducing immunogenicity to KXX in a patient. In some embodiments, co-administration of KXX and MTX results in “reducing” immunogenicity to KXX, indicating that the patient does not produce anti-KXX antibodies, or produces fewer anti-KXX antibodies than would be expected for a patient not receiving the same treatment. “Reducing” may also refer to a reduction in disease symptoms as a result of KXX treatment, either alone, or co-administered with MTX. “Reducing” immunogenicity to KXX may also be referred to herein as increasing or enhancing “immuno-tolerance.”

As used herein, “relatedness” or “causality” assessment is required for AEs (and SAEs) that occur during clinical investigations. The following terms were used during this study:

Likely: Reasons to consider an AE likely related to treatment may include but are not limited to the following: (1) Timing of the event relative to the administration of the investigational product. (2) Location of the AE relative to the site of investigational product administration. (3) Likelihood based on experience with similar products. (4) There is a biologically plausible explanation based on the mechanism of action or mode of delivery of the treatment. (5) The AE is repeated on subsequent treatments. (6) No other explanation is likely.

Quality-of-Life Assessment: The HAQ was administered at the Screening and Week −4 or week −6 (prior to the first dose of MTX) Visits during the MTX Run-in Period for the open-label and randomized studies, respectively; prior to pegloticase infusion at the Day 1 and Weeks 14, 24 and 36 Visits or at the Day 1 and weeks 6, 14, 20, 24, 30, 36, and 44 visits during the Pegloticase+IMM Period for the open-label and randomized studies, respectively; at the End of Pegloticase Infusions Visit (if applicable), the Week 52/End of Study/Early Termination Visit and the Post Treatment Periods 3 and 6 Month Follow-up Visits (open-label study). The HAQ-DI is a self-report functional status instrument that can be filled out by a subject in less than 5 minutes and requires 1 minute to score. The index measures disability over the past week by asking a total of 20 questions covering 8 domains of function: dressing and grooming, arising, eating, walking, hygiene, reach, grip, and usual activities. There are at least 2 questions in each domain and the 8 domains represent a comprehensive set of functional activities. The HAQ-DI is calculated by scoring the answer to each question in the HAQ from 0 to 3, with 0 representing the ability to do without any difficulty, and 3 representing inability to do. Any activity that requires assistance from another individual or requires the use of an assistive device raises a 0 or 1 score to a 2. The highest score for each of the 8 domains is summed (range from 0 to 24) and divided by 8 to yield, on a scale with 25 possible values, a Functional Disability Index with a range from 0 to 3. The disability index is based on the number of domains answered and is computed only if the subject completes answers to at least 6 domains. The HAQ pain scale asks subjects to record how much pain they have had in the past week on a scale of 0 to 100, where zero represents “no pain” and 100 represents “severe pain”. The HAQ health scale is a measure of overall health. Subjects are asked to rate how well they are doing on a score of 0 to 100, where zero represents “very well” and 100 represents “very poor” health.

Safety Variables: Safety was assessed via AE and concomitant medication use monitoring, physical examinations, vital signs, clinical safety laboratory evaluations (hematology, chemistry, urine uric acid:creatinine ratio), pregnancy testing (if applicable), electrocardiograms (ECGs), and AEs of special interest (i.e., IRs, anaphylaxis, gout flares, and cardiovascular events).

As used herein, a “severe adverse event” or “severe AE” refers to a sign, symptom, or event that causes severe discomfort to the participant and significantly affects clinical status or the ability to perform usual life activities, whether the event is considered related to the study drug or not. In some embodiments, treatment intervention may be warranted for a severe AE.

Examples of an AE include: (1) Conditions newly detected or diagnosed after the signing of the ICF, including conditions that may have been present but undetected prior to the start of the study; (2) Conditions known to have been present prior to the start of the study that worsen after the signing of the ICF; (3) Signs, symptoms, or the clinical sequelae of a suspected drug interaction; (4) Signs, symptoms, or the clinical sequelae of a suspected overdose of either investigational product or a concomitant medication (overdose per se was not reported as an AE). AEs of special interest may include IRs, anaphylaxis, gout flares, and cardiovascular events.

Severity in accordance with the disclosure is reported according to the following: Grade 1 (Mild)—No interference with daily activity. Grade 2 (Moderate)—Some interference with daily activity but medical intervention not required (e.g., doctor visit and/or medication); over the counter medicine permitted. Grade 3 (Severe)—Prevents daily activity and requires medical intervention (e.g., doctor visit and/or medication). Grade 4 (Potentially Life-threatening)—Emergency room visit or hospitalization.

As used herein, “stopping rule” refers to subjects with an SUA >6 mg/dL at 2 consecutive study visits beginning with the week 2 visit (not including post-infusion samples). Individuals for whom this condition is met discontinued treatment and remained in the study.

As used herein, “subject” or “individual” or “patient” refers to any patient for whom or which therapy is desired, and generally refers to the recipient of the therapy.

As used herein, a “temporary stop” refers to a short-term interruption in a dosing regimen as described herein, such as for KXX and/or MTX. A temporary stop typically lasts 2 to 4 weeks, after which the patient or subject resumes taking the drug or discontinues the drug completely. For example, as provided in Table 1, a patient taking MTX as described herein, and for whom WBC levels fall below 3×10⁹/L, was instructed to stop taking MTX for a short period of time. Following a temporary stop, the patient or subject may either resume taking the drug or may be instructed to discontinue the drug completely.

Tender and Swollen Joint Counts: Tender and swollen (excludes hip) joint counts were recorded at the Week −4 or week −6 (prior to the first dose of MTX) Visit during the MTX Run-in Period for the open-label and randomized studies, respectively; prior to pegloticase infusion at the Day 1 and Weeks 14, 24 and 36 Visits, or at the Day 1 and weeks 6, 14, 20, 24, 30, 36, and 44 visits during the Pegloticase+IMM Period for the open-label and randomized studies, respectively; and at the End of Pegloticase Infusions Visit (if applicable) and the Week 52/End of Study/Early Termination Visit and the Post Treatment 3 and 6 month Follow-up visits. Tender and swollen joint counts were assessed by physical examination.

As used herein, a “tolerizing dosage regimen” refers to a dosage or treatment regimen with KXX that induces immunological tolerance to the drug. A tolerizing dosage regimen prevents the loss of response to a drug in a patient by preventing the formation of anti-KXX antibodies. A tolerizing dosage regimen may also decrease the incidence of IRs associated with the drug.

The terms “treating” and “treatment” as used herein refer to reduction in severity and/or frequency of symptoms, elimination of symptoms and/or underlying cause, and improvement or remediation of damage. In certain aspects, the term “treating” and “treatment” as used herein refer to the prevention of the occurrence of symptoms. In other aspects, the term “treating” and “treatment” as used herein refer to the prevention of the underlying cause of symptoms associated with obesity, excess weight, and/or a related condition. The phrase “administering to a patient” refers to the process of introducing a composition or dosage form into the patient via an art-recognized means of introduction.

As used herein, “trough” refers to the lowest concentration of a drug in a patient before the next dose of the drug is administered. For example, trough KXX levels refer to the lowest levels of KXX in a patient before the next infusion of KXX. Trough levels may be used by clinicians or practitioners to determine the efficacy of the drug, or the response of the patient to the drug treatment. Trough levels of KXX or MTX may be determined or measured at any point during a treatment period as described herein, such as before any infusion of KXX, or before any administration of MTX.

As used herein, an “unexpected adverse event” or “unexpected AE” refers to any AE, the specificity, frequency or severity of which is not consistent with either: The known or foreseeable risk of AEs associated with the procedures involved in the research that are described in the protocol-related documents, such as the IRB-approved research protocol, any applicable investigator brochure, the current IRB-approved informed consent document, and other relevant sources of information (e.g., product labeling and package inserts); or the expected natural progression of any underlying disease or condition of the participant(s) experiencing the AE.

Unlikely: An AE with no temporal association with the study drug but rather related to other etiologies such as concomitant medications or conditions, or subject's known clinical state.

Vital Signs, Height, and Weight: Routine vital signs, including blood pressure, respiratory rate, temperature, and heart rate were measured at Screening, Week −4 and at all infusion visits during the Pegloticase+IMM Period and the End of Pegloticase Infusions Visit (if applicable), Week 52/End of Study/Early Termination and 3- and 6-month Post Treatment Follow-up Visits for the open-label study. For the randomized study, such measurements were taken at Screening, Week −6, Week −4, Day 1 and Weeks 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, 34, 36, 38, 40, 42, 44, 46, 48, 50 and the End of Pegloticase Infusions Visit (if applicable), Week 52/End of Study/Early Termination and 3 and 6 month Post Treatment Follow-up Visits.

For the randomized study, at sites who participate and from subjects who consent, optional intensive blood pressure measurements were taken prior to the infusion on Day 1 and at Weeks 6, 12, 18, 24, 30, 36, 42, 48 and at the non-infusion End of Pegloticase Infusions Visit (if applicable) and Week 52/End of Study/Early Termination Visit. At these intensive blood pressure collections, three blood pressure measurements were performed, at least 2 minutes apart, with BP readings measured to the nearest mm Hg prior to pegloticase infusion. If any of the 3 systolic blood pressure measurements differed by more than 8 mm Hg or if diastolic measurements differed by more than 5 mm Hg, a second set of 3 sitting blood pressure measurements were obtained.

During the Pegloticase+IMM Period study visits, vitals were taken before the pegloticase infusion and any time after the end of the infusion, but prior to subject's discharge/release from the site. Weight was measured in kilograms or pounds without shoes and recorded at the Screening Visit; prior to pegloticase infusion on Day 1 and at the Weeks 8, 16, 24, 36 and at the non-infusion End of Pegloticase Infusions Visit (if applicable), Week 52/End of Study/Early Termination and Months 3 and 6 Post Treatment Follow-up Visits.

X-ray of hands and feet: For sites with X-ray capability, and subjects who provide consent, an optional X-ray of the hands and feet was obtained at Day 1, Week 24 and End of Pegloticase Infusions Visit (if applicable) and Week 52/End of Study/Early Termination Visit for the randomized study.

Subjects who end pegloticase infusions prior to Week 52 followed the scheduled timepoints but avoided a repeat X-ray within 3 months of a prior X-ray (detailed guidance was provided with the imaging manual).

EXAMPLES

Examples of embodiments of the present disclosure are provided in the following examples. The following examples are presented only by way of illustration and to assist one of ordinary skill in using the disclosure. The examples are not intended in any way to otherwise limit the scope of the disclosure.

Example 1

Study Design

The disclosure describes a study in subjects initiating pegloticase for treatment of chronic refractory gout. The purpose of the present study was to determine the efficacy and safety of using immune modulating therapy with MTX to prevent immunogenicity conferred by pegloticase and to enhance the response rate seen with pegloticase alone in adults with uncontrolled gout.

This was a multicenter, open-label, efficacy and safety study of pegloticase with MTX in adult subjects with uncontrolled gout.

The study design included: (1) up to a 2-week Screening Period (screening was completed within 2 weeks prior to Week −4); (2) a 4-week MTX Run-in Period (week −4 through day 1); (3) a 52-week Pegloticase+MTX Period (day 1 through week 52), MTX dosed weekly and 50 weeks of KXX infusions visits every 2 weeks; non-infusion visits at Weeks 1, 7 and 52); (4) a Safety Follow-up (Phone/Email/Site Visit); and (5) a 3- and 6-month Post Treatment Follow-up.

In addition, if applicable, the following additional study periods applied:

End of Pegloticase Infusions Visit—completed within approximately 2 weeks of the last infusion if the subject discontinued pegloticase treatment prior to infusion Week 50, such as due to the SUA stopping rules. Subjects continued in the study.

Week 52/End-of-study/Early Termination Visit: Week 52 or earlier if the subject withdrew consent to participate in the study.

Safety Follow-up Visits: All subjects received a safety follow-up phone call/e-mail/visit approximately 30 days after the last dose of pegloticase/MTX to assess if any SAE's had occurred. Subjects who received at least one dose of MTX and were females of childbearing potential, received a safety follow-up phone call/e-mail/Site Visit approximately 30 days after the last dose of MTX to verify at least one ovulatory cycle occurred after the last dose of MTX. If the subject had not ovulated, a urine pregnancy test was performed. Subjects who received at least one dose of MTX and were non-vasectomized males, a phone/e-mail/Site Visit inquiry was conducted 3 months after MTX discontinuation regarding partner pregnancy (inquiry could occur during the 3-month Post Treatment Follow-up).

3- and 6-Month Post Treatment Follow-up Visits: All subjects were followed for a minimum of 6 months following the last infusion, with follow-up after Week 52 as warranted.

All subjects who meet eligibility criteria at Screening began oral MTX at a dose of 15 mg weekly on the same day each week for 4 weeks prior to the first dose of KXX. During the KXX+MTX period, subjects were instructed to take MTX weekly on the same day each week within 1 to 3 days prior to each KXX infusion and one additional weekly dose after the last infusion for subjects who had not stopped pegloticase due to SUA stopping rules; however, if a subject does not do so, MTX were taken ≥60 minutes prior to each pegloticase infusion.

The subjects also took folic acid 1 mg orally every day beginning at Week −4 (the start of MTX) continuing until prior to the Week 52/End of Study/Early Termination Visit. Subjects had to be able to tolerate MTX at a dose of 15 mg during the 4-week MTX Run-in Period (prior to Day 1) to be eligible to participate in the KXX+MTX Period. Subjects who were unable to tolerate MTX at a dose of 15 mg during the MTX Run-in Period were considered screen failures.

As used herein, a “screen failure” refers to a subject who does not meet all the inclusion criteria or meet any of the exclusion criteria. In addition, subjects who were unable to tolerate MTX at an oral dose of 15 mg weekly during the MTX Run-in Period were considered screen failures. Screen failure subjects who were females of childbearing potential who took at least one dose of MTX, received a Safety Follow-up Phone call/E-mail/Site Visit approximately 30 days after the last dose of MTX to verify at least one ovulatory cycle after the last dose of MTX. If the subject had not ovulated, a urine pregnancy test was performed at the study site. Screen failure subjects who receive at least 1 dose of MTX and were non-vasectomized males received a Phone/E-mail/Site Visit 3 months after MTX discontinuation regarding partner pregnancy.

Screen failure subjects may be allowed to rescreen for the study if both the Investigator and Sponsor agree regarding rescreening and if the Investigator determines that the subject can satisfy all the eligibility criteria.

During the MTX Run-in or Tolerability assessment period, a subject was considered a screen failure if any of the following new laboratory findings or symptoms reflecting MTX immunogenicity occur:

Abnormal Hematology Findings:

-   -   WBC<3.5×10⁹/L     -   Platelets<75×10⁹/L Hematocrit <32%

Abnormal Hepatic Function Findings:

-   -   AST/ALT>1.5× upper limit of reference range and     -   Albumin<lower limit of reference range

Abnormal renal function: eGFR <40 mL/min/1.73 m² (as estimated with the MDRD equation)

New clinically important signs and symptoms, such as the following:

-   -   Rash or oral ulceration     -   Persistent nausea, vomiting and diarrhea     -   New or increasing dyspnea or dry cough, or unexplained cough         with fever     -   Severe sore throat, abnormal bruising     -   Severe headaches, fatigue, and problems concentrating

If minor clinical symptoms emerge, such as mild stomatitis, mild GI discomfort, etc., the investigator may increase folic acid dose (e.g., 2 mg daily) or recommend a divided dose of MTX (e.g., 3 tabs of 2.5 mg in the morning and evening on the day of dosing); if symptoms improve, subject were not considered a screen failure based on that symptom.

During the Run-In and Pegloticase+IMM Period, MTX or placebo dose guidance based on new laboratory findings or new symptoms is as follows:

Lab Parameters Value MTX Dose Change WBC  3.0 × 10⁹/L~3.5 × 10⁹/L Decrease to 10 mg <3.0 × 10⁹/L Temporary stop Platelets  <50 × 10⁹/L Temporary stop Hematocrit <27% Temporary stop AST/ALT Between 1.5~2 × ULN Decrease to 10 mg   >2 × ULN Temporary stop eGFR <30 ml/min/1.73 m² Temporary stop New clinically Yes Temporary stop important symptoms/ signs*

New clinically important symptoms or important medical events may include rash or oral ulceration, persistent nausea, vomiting and diarrhea, new or increasing dyspnea or dry cough, or unexplained cough with fever, severe sore throat, abnormal bruising, severe headaches, fatigue, and problems concentrating, or any other important medical events that might increase methotrexate toxicity or pre-dispose to new or worsening infection (e.g., undergoing surgery, hospitalization, being treated with antibiotics, having a clinical infection, developing new clinically significant pericardial/pleural effusion or ascites).

Any other important medical events that might increase methotrexate toxicity or pre-dispose to new or worsening infection (e.g., undergoing surgery, hospitalization, being treated with antibiotics, having a clinical infection, developing new clinically significant pericardial/pleural effusion or ascites)

Subjects who take at least one dose of MTX and who were females of childbearing potential, received a safety follow-up phone call/e-mail approximately 30 days after the last dose of MTX to verify at least one ovulatory cycle had occurred after the last dose of MTX. If the subject had not ovulated, a urine pregnancy test was performed. For those subjects who took at least one dose of MTX and who were non-vasectomized males an inquiry was conducted at the Post-Treatment 3-month follow-up visit (or 3 months after the subject's last dose of MTX) after MTX discontinuation regarding partner pregnancy.

All subjects who complete the Run-In Period received the first pegloticase infusion on Day 1. All subsequent doses and study visits were scheduled based on the Day 1 visit date.

After Day 1, if a subject became unable to tolerate 15 mg of MTX, the MTX dose was reduced and/or discontinued, and the subject remained in the study.

The study followed each participant from screening for up to one year until completion of the full study. Participants were randomized to either pegloticase+MTX (Peg+MTX) or to pegloticase+placebo (peg+PBO). Randomization allocation were balanced in time and by site to achieve the desired number of participants. Treatment assignment were determined by a random number generator and stratified by site using a central randomization system to ensure the desired allocation. During the first 12 weeks, participants randomized to the peg+MTX arm received a combination of pegloticase and MTX. Patients experience reduced immunogenicity when a loading dose of anti-proliferative agent is administered prior to a monoclonal antibody in other disease states, thus, for those randomized to the KXX+MTX arm, a MTX run-in may be begun prior to initial pegloticase infusion. MTX (or matching PBO in the other arm) was administered concurrent with the first pegloticase infusion. Next, infusions of pegloticase 8 mg IV were administered on a biweekly basis. To understand the long-term efficacy (durability) and safety of this approach, and to minimize the exposure to MTX, following the study, all participants may be given an additional three months of open-label pegloticase only therapy and were followed.

Each subject was followed up for at least 6 months after cessation of pegloticase infusions. If these 6 months occur prior to end of study at Week 52, such as in the case of a subject who ends pegloticase infusions on or before Week 24, there were no follow-up visits after the Week 52/End of Study Visit. For subjects who end pegloticase infusions between Weeks 26 and 36, there were at least 3 months of follow-up while the subject remains on-study prior to Week 52, and then one follow-up visit after the Week 52/End of Study Visit. For subjects who end pegloticase infusions between Weeks 38 and 52, there were two follow-up visits at intervals of 3 months after the Week 52/End of Study Visit.

The Investigator reviewed the clinical status and individual subject treatment goals at Week 24, and the End of Pegloticase Infusions Visit (if applicable) and the Week 52/End of study/Early Termination Visit.

Samples for measurement of SUA levels, PK analysis of pegloticase, pegloticase immunogenicity and MTX Polyglutamate analysis were collected at periodic visits as set forth herein.

Safety assessments, including monitoring and recording of all ΔEs, whether drug-related or not, measurement of vital signs, physical examinations, and monitoring of hematology and blood chemistry, were performed.

Criteria for Evaluation: Efficacy was assessed by SUA levels, tender and swollen joint counts, patient and physician global assessments of gout, joint pain, and DECT.

Quality of life was assessed using the HAQ.

The PK of pegloticase and pegloticase immunogenicity as assessed by the incidence of anti-PEG and anti-uricase IgG antibodies were assessed at specified time points.

Safety assessments included monitoring and recording of all AEs, whether drug-related or not, measurement of vital signs, physical examinations, and monitoring of hematology and blood chemistry.

A scientific advisory group consisting of 3 physicians (2 site physicians and 1 Sponsor physician) and a Sponsor statistician provided oversight for the overall directions and strategy for the study and met periodically during the study.

If the study drug is discontinued, unless the subject withdraws consent, the subject was followed for the full study period and all data were collected as scheduled. Participants that were lost to follow-up or withdraw and were not evaluable were replaced. This may include but is not limited to the following reasons:

-   -   The subject deciding to withdraw consent for study     -   An intolerable adverse event (AE) as judged by study site PI and         participant     -   The subject discontinuing acceptable birth control methods or         becoming pregnant     -   The subject enrolling in a conflicting investigational drug         trial.

Example 2

Study Outcomes/Objectives

The overall objective of the study is to assess the efficacy, safety, tolerability, and pharmacokinetics (PK) of the concomitant use of KXX with MTX to enhance the response rate seen with pegloticase alone in adults with uncontrolled gout.

Primary Objectives/Outcomes

The primary objective is to estimate the response rate during Month 6 (Weeks 20, 22, and 24), as measured by the sustained normalization of serum uric acid (SUA) to <6 mg/dL for at least 80% of the time during Month 6 in subjects receiving KXX with MTX.

The primary efficacy outcome endpoint is the sustained normalization of SUA to <6 mg/dL for at least 80% of the time during month 6 (weeks 20, 22, and 24) in subjects receiving KXX with MTX. This is slightly below the urate solubility threshold and this threshold has been the accepted standard for nearly all modern gout trials. Participants who achieve this endpoint were classified as “responders.” Serum uric acid (SUA) responders may also be defined as participants achieving and maintaining SUA <6 mg/dL for at least 80% of the time during Month 6 (Weeks 20, 22, and 24).

Blood samples may be collected prior to each pegloticase infusion for measurement of SUA levels using the Beckman Coulter AU System Uric Acid procedure. Participants were declared “non-responders” if there were SUA measures >6 mg/dL at 2 consecutive study visits beginning with the week 2 visit. Participants who had a single SUA >6 mg/dL were allowed to continue (per the prescribing information) and were considered a responder. If the SUA goal is not maintained before or at the 12-week mark, it was assumed that the participant had developed clinically relevant anti-pegloticase antibody and they received no further infusions. This assumption and subsequent discontinuation of pegloticase was consistent with the protocol of large phase III randomized controlled trials and the product label. A formal stopping rule was 2 occasions of SUA levels of greater than 6 mg/dL.

Safety assessments were made throughout the procedure. Safety assessments may include monitoring and recording of all AEs, whether drug-related or not, regular measurement of vital signs, performance of physical examinations and monitoring of hematology and blood chemistry. In the event of an AE suspected to be an IR, a blood sample was collected at that time or the subsequent visit, centrifuged, frozen and stored for the batch evaluation of pegloticase antibodies at a future date. Gout flares were captured as safety events only.

Secondary Objectives/Outcomes

Secondary endpoints may examine anti-pegloticase Ab titers/types, different definitions of SUA level for specific later time points of success, and patient reported outcomes (PROs).

For example, in some embodiments, secondary outcomes may include one or more of the following:

Estimation of the response rate during month 3 (weeks 10, 12, and 14), as measured by the sustained normalization of serum uric acid (SUA) to <6 mg/dL for at least 80% of the time during month 3 in subjects receiving pegloticase with MTX;

Estimation of the overall response rate as measured by the sustained normalization of SUA to <6 mg/dL for at least 80% of the time during month 3 (weeks 10, 12, and 14) and month 6 (weeks 20, 22, and 24) combined in subjects receiving pegloticase with MTX;

Estimation of the 5 mg/dL response rate during month 3, during month 6, and overall (months 3 and 6 combined), as measured by the sustained normalization of SUA to <5 mg/dL for at least 80% of the time during month 3, during month 6, and months 3 and 6 combined in subjects receiving pegloticase with MTX;

Estimation of the mean change in serum uric acid from baseline to weeks 14, 24, 36, and 52 in SUA in subjects receiving pegloticase with MTX.

Exploratory Objectives/Outcomes

Exploratory objectives may include one or more of the following:

Estimation of the response rate during month 9 (weeks 32, 34 and 36), as measured by the sustained normalization of SUA to <6 mg/dL for at least 80% of the time during month 9 in subjects receiving pegloticase with MTX.

Estimation of the response rate during month 12 (weeks 48, 50 and 52), as measured by the sustained normalization of SUA to <6 mg/dL for at least 80% of the time during month 12 in subjects receiving pegloticase with MTX.

Estimation of the 5 mg/dL response rate during Month 9 (Weeks 32, 34 and 36), as measured by the sustained normalization of SUA to <5 mg/dL for at least 80% of the time during Month 9 in subjects receiving pegloticase with MTX.

Estimation of the 5 mg/dL response rate during Month 12 (Weeks 48, 50 and 52), as measured by the sustained normalization of SUA to <5 mg/dL for at least 80% of the time during Month 12 in subjects receiving pegloticase with MTX.

Estimation of the time to first SUA >6 mg/dL in subjects receiving pegloticase with MTX.

Estimation of the time to SUA >6 mg/dL (stopping rule) at 2 consecutive study visits beginning with the week 2 visit (not including post-infusion samples) in subjects receiving pegloticase with MTX.

Estimation of the mean change from baseline to Week 24, 36 and 52 in urate volume and gout erosions using dual-energy computed tomography (DECT) scan of the hands and feet in subjects receiving pegloticase with MTX.

Estimation of the mean change from baseline in number of joints affected by tophi in subjects receiving pegloticase with MTX.

Estimation of the mean change from baseline to Weeks 14, 24, 36, and 52 in tender joint count (68-point scale) in subjects receiving pegloticase with MTX.

Estimation of the mean change from baseline to Weeks 14, 24, 36, and 52 in swollen joint count (66-point scale) in subjects receiving pegloticase with MTX.

Estimation of the mean change from baseline to Weeks 14, 24, 36, and 52 in the Health Assessment Questionnaire—Disability Index (HAQ-DI) in subjects receiving pegloticase with MTX.

Estimation of the mean change from baseline to Weeks 14, 24, 36, and 52 in the HAQ Pain score in subjects receiving pegloticase with MTX.

Estimation of the mean change from baseline to Weeks 14, 24, 36, and 52 in the HAQ Health score in subjects receiving pegloticase with MTX.

Estimation of the mean change from baseline to Weeks 14, 24, 36, and 52 in patient global assessment of gout in subjects receiving pegloticase with MTX.

Estimation of the mean change from baseline to Weeks 14, 24, 36, and 52 in physician global assessment of gout in subjects receiving pegloticase with MTX.

Estimation of the mean change from baseline to Weeks 14, 24, 36, and 52 in subject assessment of average, least, and worst joint pain in subjects receiving pegloticase with MTX.

Estimation of the proportion of subjects achieving 20%, 50%, or 70% improvement based on gout chronic response criteria at Weeks 14, 24, 36, and 52 in subjects receiving pegloticase with MTX.

Pharmacokinetic and Anti-Drug Antibody Objectives/Outcomes

Assessment of the PK of pegloticase in subjects receiving concomitant MTX.

Assessment of the incidence of anti-PEG and anti-Uricase IgG antibodies.

Safety and Tolerability Objectives/Outcomes

Safety and Tolerability objectives/outcomes may include assessment of the incidence of infusion reactions (IRs), anaphylaxis, gout flares, cardiovascular events, and the adverse event (AE)/serious AE profile overall and potentially attributed to the combination of pegloticase and MTX.

Example 3

Laboratory Evaluations

Any or all the following measurements may be assessed for each patient, and at any desired time points during the study.

Hematology—Blood was collected for measurement of hemoglobin concentration, hematocrit, erythrocyte, platelet and leukocyte counts and the differential leukocyte count at screening, and end of treatment or early termination visit.

Clinical Chemistry—Blood samples were collected prior to each pegloticase infusion for measurement of SUA levels (primary efficacy parameter) using the Beckman Coulter AU System Uric Acid procedure. In this procedure uric acid is converted to hydrogen peroxide. Hydrogen peroxide reacts with reagent to produce a chromophore which is read bichromatically at 660/800 nm. The amount of dye formed is proportional to the uric acid concentration in the sample.

Serum samples for measurement of SUA levels were collected at the Screening Visit, the Week −4 Visit (prior to the first dose of MTX), and the Week -2 Visit during the MTX Run-in Period; within 48 hours prior to each pegloticase infusion and after the end of each pegloticase infusion prior to discharge from the site during the Pegloticase+IMM Period; at the non-infusion Week 52/End of Study/Early Termination Visits and at the Post Treatment 3 and 6 Month Follow-up Visits. Additional serum samples for SUA levels were collected at optional non-infusion (Frequent Sampling) Visits at Weeks 1 and 7. If applicable an SUA sample was collected at the End of Pegloticase Visit if a subject did not continue treatment. Subjects with SUA level >6 mg/dL at 2 consecutive visits beginning at Week 2 visit discontinued treatment, completed the End of Pegloticase Infusion Visit procedures within 2 weeks and continued the subject visits according to the protocol (without treatment).

Samples for measurement of SUA levels, PK analysis of pegloticase, pegloticase immunogenicity, and MTX Polyglutamate analysis were collected at specific visits during the treatment regimen.

Safety assessments, including monitoring and recording of all AEs, whether drug-related or not, measurement of vital signs, physical examinations, and monitoring of hematology and blood chemistry, were performed.

The total blood volume to be collected from each subject during this study is approximately 700 mL, increased to 750 mL for the subjects participating in the optional visits at Week 1 and Week 7.

Blood was collected for measurement of transaminases (AST, ALT), alkaline phosphatase, total bilirubin, lactic dehydrogenase (LDH), creatinine, uric acid, glucose, total cholesterol, sodium, potassium, calcium, chloride, total protein, and blood urea nitrogen (BUN) at Screening and end of treatment or early termination visit).

A blood sample was obtained at Screening to evaluate Glucose-6-Phosphate Dehydrogenase (G6PD). G6PD deficiency was an exclusion criterion.

Anti-pegloticase Antibody Assay Development—The presence or absence of antibodies was examined in all participants at the following time point, whichever is earlier: 1) achieve non-responder status or experiencing an IR, or 2) for responders. Anti-pegloticase antibody titers were determined by an enzyme-linked immunosorbent assays (ELISA) upon development of an immune reaction or loss of responder status. We collected and stored all serum samples for future batch analyses.

ELISA plates were coated with pegloticase, recombinant uricase, or polyethylene glycol (PEG) (5 μg/mL each) as the capture antigen, respectively, at 3720 C. for 2 hrs. The plates were then washed with phosphate-buffered saline—Tween-20 (PBS—T) and blocked for 60 min with PBS—T plus 3% milk (PBS—T milk). Sera were diluted (1:30 for the anti-pegloticase or anti-uricase assay; and 1:10 for the anti-PEG assay) in PBS—T milk, were transferred to the plates and incubated for 45 min at room temperature. The plates were then incubated with horseradish peroxidase (HRP)-conjugated isotype-specific goat anti-human immunoglobulin −G (IgG) or goat anti-human immunoglobulin-M (IgM) (Southern Biotechnology Associates, Birmingham, Ala., USA) at 3720 C. for 1 hr. Color development was performed by using 3,3′,5,5′-tetramethylbenzidine (TMB) as the substrate. The reaction was stopped by means of acidification and the plate was read at 450 nm by using an Emax Precision Microplate Reader (Molecular Device, Sunnyvale, Calif., USA).

Positive Controls for the Anti-Pegloticase ELISA Assay

For the anti-pegloticase assay, a ‘positive’ ELISA response was initially defined as an ELISA optical density A₄₅₀ greater than 3 SD above the mean for baseline pretreatment plasma samples from study subjects. Results were further compared with those obtained from a panel of healthy control sera. Positive samples were further validated by the specificity and sensitivity assays. Established sero-positive samples were used as positive control for subsequent assays. The positive control for the anti-uricase antibody assay was the monoclonal mouse anti-uricase antibody (Santa Cruz Biotechnology, Inc.). The positive control for the anti-PEG assay was the monoclonal mouse anti-PEG antibody (Academia Sinica, Taiwan).

Determination of Anti-Pegloticase Antibody Titers and Seropositivity

For determination of Ab titers, those serum samples found to contain detectable Ab were subjected to serial 3-fold dilutions in normal serum and analyzed in duplicate. The final titer for each sample was defined as the highest dilution of serum that produced a mean absorbance (A₄₅₀ nm) greater than the negative cut-off value. Antibody seropositivity was further defined as absorbance at 450 nm, >3 SD above the mean for a panel of plasma samples from naive patients.

An enzymatic/fluorescence assay was used to quantitate pegloticase concentrations in serum. In the assay, pegloticase catalyzes the conversion of UA to allantoin, thus releasing hydrogen peroxide (H₂O ) and carbon dioxide. In the presence of horseradish peroxidase, H₂O₂ reacts with a 1:1 stoichiometry with Amplex Ultra Red (Molecular Probes, Inc., Eugene, Oreg.) to generate the red fluorescence oxidation product, resorufin. The concentration of resorufin, which is determined by fluorometry, is proportional to the amount of active pegloticase present in the serum samples. The lower limit of detection established in previous studies has been determined to be 0.6 μg/mL.

Validation of the Anti-Pegloticase ELISA Assays

Validation included negative cut-off and cut-point factor determinations, as well as tests for intra and inter-assay precision, sensitivity, specificity and recovery, stability (bench top, freeze-thaw cycles, long-term), drug interference, prozone effect and drug competition. In previous studies the sensitivity of the anti-pegloticase Ab assay was 7.5 μg/mL for the enzyme portion and 23 ng/mL for the PEG moiety using purified rabbit anti-uricase and purified mouse anti-PEG positive controls.

Validation of anti-PEG was carried out by determination of assay sensitivity, working range, dilutional linearity, spiking recovery, intra-assay variability, and inter-assay variability using systematic ELISA validation methods. These were carried out with the use of selected samples diluted 1:200 or 1:20 with PBS, pH 7.2, containing 1% BSA and 0.05% Tween 20. Samples used for assay validation were stored at −20° C. until used. Sensitivity was determined by calculating the mean response of 10 sets of blanks and evaluating the mean plus 3 standard deviations on the standard curve. The lower limit of the working range was defined as the sensitivity. The upper limit of the working range was determined by the apparent value of an absorbance, which equals the mean maximum absorbance minus 3 standard deviations, as determined from the mean absorbance in 10 duplicate wells containing approximately 7.5 μg/mL of pegloticase 7.5 μg/mL for the enzyme portion and 23 ng/mL for the PEG moiety. For validation of the assay at different dilutions, at least 4 serum samples were diluted 1:200 and 2 serum samples diluted 1:20. All serum samples were single random samples. Dilutional linearity was determined by evaluating each sample at its initial strength (1:200 or 1:20) and at dilutions of 1:2, 1:4, and 1:8. Spiking recovery was determined by adding 0.0, 0.0125, 0.025, 0.050, 0.100, 0.200, and 0.400 μg/L of pegloticase to each of the diluted serum samples. Intra-assay variability was determined by evaluating the 7 diluted serum samples 10 times within the same assay run [% CV=(standard deviations/mean)*100, where CV=coefficient of variation]. Inter-assay variability was determined by evaluating the 7 diluted serum samples in 10 consecutive assay runs [% CV=(standard deviations/mean)*100].

Competition assays to determine the specificity of anti-pegloticase Ab and anti-uricase Ab, a variety of PEGylated proteins, including pegloticase (˜40 PEGs/protein molecule; molecular weight 545 kDa), PEG-asparaginase (˜40 PEGs/protein molecule; 340 kDa), PEG-catalase (˜40 PEGs/protein molecule; 440 kDa), PEG-chymotrypsin (˜9 PEGs/protein molecule; 70 kDa), PEG-subtilisin (˜6 PEGs/protein molecule; 57 kDa) and PEG-superoxide dismutase (˜10 PEGs/protein molecule; 82 kDa) were used in competition assays. All the proteins except for pegloticase were modified with 5 kDa PEG from Sigma-Aldrich (St Louis, Mo.). Serum from anti-pegloticase sero-positive samples were diluted 1:30 and assayed for Ab in pegloticase-coated ELISA wells in the presence or absence of 200 μg/mL of the various soluble PEGylated proteins. A mixture of lysozyme (50 μg/mL) and propylene oxide (150 μg/mL) were used as a negative control. Also, non-PEGylated proteins were included as the non-competitive controls. To confirm the specificity of the anti-uricase Ab assay, uricase 2 μg/mL (or 2 μg/mL lysozyme for the negative control) were added during the serum incubation step.

Example 4

Participant Population

We recruited and enrolled patients or subjects with SUA ≥6 mg/dL diagnosed with chronic refractory gout that failed to normalize SUA and whose signs and symptoms were inadequately controlled with oral ULT at the maximum medically appropriate dose or the xanthine oxidase inhibitor needs to be contraindicated (FDA indication for pegloticase). Recruitment includde men and women of all races/ethnicities. Approximately 12-17 patients were enrolled in the study. This number may change as deemed necessary by the study director.

The primary efficacy endpoint, the proportion of subjects achieving and maintaining SUA <6 mg/dL for at least 80% of the time during Month 6 (Weeks 20, 22, and 24) of the Pegloticase+MTX Period, were demonstrated to be statistically greater than 43.5% (proportion of responders during Month 6 in phase 3 studies), according to an exact test for proportions with a 5% type I error, if at least 10/13 (77%) responders were observed; in that case, the lower bound of a 95% confidence interval for the proportion of responders was about 46%.

Inclusion Criteria

Men and women ≥18 years of age. Participants may also be selected based on an age range between 18 and 65 years of age.

Hyperuricemic at screening visit, week −4, or week −2 of the screening or run-in period as documented by SUA ≥6 mg/dL.

Chronic refractory gout*, defined as subjects who failed to achieve a sustained SUA of <6 mg/dL and whose signs and symptoms were inadequately controlled with xanthine oxidase inhibitors at a medically appropriate dose or for whom these drugs were contraindicated. Uncontrolled gout may be defined as meeting the following criteria: SUA ≥6 mg/dL prior to entry into the KXX+MTX Period (any laboratory tests during screening up to and including during the MTX Run in Period) and at least 1 of the following: inability to maintain SUA <6 mg/dL on other urate-lowering therapy; intolerable side effects associated with current urate lowering therapy; functionally limiting tophaceous deposits (including those detected clinically or by DECT imaging).

Able to tolerate MTX at a dosage of 15 mg for 4 weeks during the Screening/MTX Run-in Period prior to the first dose of KXX.

Exclusion Criteria

Weight >160 kg (352 pounds).

Any serious acute bacterial infection, unless treated and complete resolved with antibiotics at least 2 weeks prior to the week −4 Visit of the MTX run-in period.

Severe chronic or recurrent bacterial infections (such as recurrent pneumonia, chronic bronchiectasis)

Current immunocompromised condition, including current or chronic treatment with immunosuppressive agents (prednisone or equivalent dose >5 mg/day). Prednisone >10 mg/day or equivalent dose of other corticosteroid may also exclude certain patients.

Subjects at risk for tuberculosis (TB). Specifically, subjects with i) current clinical, radiographic or laboratory evidence of active or latent TB; ii) a history of active TB within the last 3 years even if it was treated; iii) a history of active TB greater than 3 years ago unless there is documentation that the prior anti-TB treatment was appropriate in duration and type.

Known history of Hepatitis-B surface antigen-positive or Hepatitis B DNA positive subjects.

Known history of Hepatitis C RNA-positive subjects.

Human Immunodeficiency Virus (HIV) infection positive

G6PD deficiency (tested at Screening Visit 1)

Severe chronic renal impairment (glomerular filtration rate [GFR] <25 mL/min/1.73 m²) or currently on dialysis

Subjects having any transplant surgery requiring maintenance immunosuppressive therapy.

Non-compensated congestive heart failure, uncontrolled arrhythmia, treatment for acute coronary syndrome (myocardial infarction or unstable angina), or hospitalization for congestive heart failure within 3 months of screening or uncontrolled blood pressure (>160/100 mm Hg) at the end of the screening and MTX run-in period

Pregnant, planning to become pregnant, breast-feeding, or not on an effective form of birth control

Prior treatment with pegloticase, another recombinant uricase, or concomitant therapy with a polyethylene glycol (PEG)-conjugated drug

Known allergy to pegylated products or history of anaphylactic reaction to a recombinant protein or porcine product

Contraindication to MTX treatment or MTX treatment considered inappropriate

Known immunogenicity to MTX

Recipient of an investigational drug within 4 weeks or 5 half-lives prior to study drug or MTX administration or plans to take an investigational agent during the study

Current liver disease as determined by alanine transaminase ALT or aspartate transaminase (AST) levels >3 times upper limit of normal

Currently receiving treatment for ongoing cancer, excluding non-melanoma skin cancer

History of malignancy within 5 years other than skin cancer or in situ carcinoma of cervix

Uncontrolled hyperglycemia with a plasma glucose value >240 mg/dL at screening that is not subsequently controlled by the end of the Screening/MTX Run-in Period.

Diagnosed osteomyelitis

Individuals with hypoxanthine-guanine phosphoribosyl-transferase (HGPRT) deficiency such as Lesch-Nyhan and Kelley-Seegmiller syndrome

Unsuitable candidate for the study based on opinion of the Investigator (e.g., cognitive impairment) that might create undue risk to the participant or interfere with the participant's ability to comply with the protocol requirements, or to complete the study.

Alcohol use in excess of 3 alcoholic beverages per week.

Currently receiving allopurinol and unable to discontinue medication 7 days prior to MTX dosing at Week −4 and unable to discontinue treatment during the duration of the study.

Example 5

Study Procedures and Assessments

All study visits and procedures were performed at designated clinical study sites. Enrollment was competitive between sites.

Participants were seen at screening, baseline, and every two weeks thereafter for pegloticase infusion and evaluation. Blood samples prior to each pegloticase dose allowed measurement of SUA, comprehensive metabolic panel, and complete blood count (CBC) allowed appropriate measurement for the co-primary safety and secondary outcomes with respect to MTX.

Screening Visit—within 2 Weeks Prior to First Dose of MTX at Week −4

The screening visit took approximately 1 hour to complete. Potential participants were screened to determine if they satisfed all inclusion and exclusion criteria. Men and women 18 years of age or older were invited to proceed with informed consent (IC) and enroll in the study. At the screening visit, the study objectives were explained to potential participants. After all questions raised by a potential participant were answered, and before any protocol-specified screening procedures were initiated, they were offered the IC for the screening evaluation. A copy of the signed and dated IC form was provided to the participant.

After IC is obtained, a 6-digit participant number was assigned. The first 3 digits of each participant number represented the site and the last 3 were unique for each participant at each site. All screening procedures were completed, and eligibility criteria met, prior to start of immune-modulating therapy and pegloticase infusions. Basic demographic information and reason(s) for exclusion were completed on the specified case report form (CRF) pages for all participants who signed an ICF, but never received pegloticase. During the screening visit, the following procedures were performed, and information was obtained to determine eligibility to continue in this research study:

Review inclusion/exclusion criteria

ICF

Date of birth

Self-reported race/ethnicity

Medical history that might preclude study participation

Gout history and symptom severity

Medication review

-   -   Medication history (including use of over the counter         medications [e.g., aspirin], use of other prescription         medications including gout medications)     -   Dietary supplement/vitamin use

Vital signs

Physical exam includes, but is not limited to: Eye, Head, Ears, Nose, and Throat Exam (HENT), and Neck; Cardiovascular; Dermatological; Respiratory; Gastrointestinal; Musculoskeletal; Neurologic; Integumentary; VS/Measurements

Gout Flare/assessment

PROs (e.g., PROMIS-29 & GIS instrument)

Blood draw

Screening Visit Laboratory

-   -   CBC with diff     -   HIV1 and 2 Antibody Screen     -   IgG     -   SUA     -   Pregnancy test for premenopausal women     -   Comprehensive Metabolic Panel (CMP)     -   G6PD     -   Blood sample for serum banking

Vital signs consisted of heart rate, respiratory rate, blood pressure (noting the position in which it was obtained), and body temperature (taken either orally or aurally). All measurements of pulse rate and blood pressure were made after approximately 5 minutes of rest. Focused history and physical examination: Information collected included date of birth, self-reported race/ethnicity (defined as in previous studies investigating its role in rheumatic diseases, gout history, medication history (including use of aspirin, gout medications), weight, and height.

Assessments for presence of tophi were conducted as well as gout history and symptom severity.

Document the number of gout flares in the last 6 months and 12 months and the most recent occurrence. Patients with gout flares can enter the study if the flare treatment is discontinued 1 week prior to the first dose of pegloticase.

Document the presence and/or history of gout-related kidney disease.

Physical examinations were performed by body system at Screening and Week 24 (end of treatment) or early termination visit in the pegloticase dosing phase. Significant findings prior to the administration of pegloticase were recorded in the patient's medical record and included on the Medical History in the CRFs. Significant findings that occur after administration of pegloticase which meet the definition of an AE were recorded in the medical record and on the Adverse Events CRF page.

All women of childbearing potential must use an effective form of birth control during this study and for 30 days after completion of the study. Acceptable methods of birth control include hormonal control methods, inter-uterine device, a double-barrier method (diaphragm with spermicide, condom with spermicide) or abstinence. All male participants were cautioned to use proper birth control methods with their partners during the study in which MTX is received.

Women of childbearing potential (including those with an onset of menopause <2 years prior to screening, non-therapy-induced amenorrhea for <12 months prior to screening, or not surgically sterile [absence of ovaries and/or uterus]) must have negative serum/urine pregnancy tests during the Screening/MTX Run in Period; participants may be required to use 2 reliable forms of contraception during the study, one of which is recommended to be hormonal, such as an oral contraceptive. Hormonal contraception were started ≥1 full cycle prior to Week −4 (start of MTX dosing) and continue for 30 days after the last dose of KRYSTEXXA®. Highly effective contraceptive methods (with a failure rate <1% per year), when used consistently and correctly, include implants, injectables, combined oral contraceptives, some intrauterine devices, sexual abstinence, or vasectomized partner. Men who were not vasectomized must agree to not impregnate their female partner during the study and for at least 3 months after the last dose of MTX.

Laboratory: SUA, CMP, CBC with diff, and pregnancy test for premenopausal women. Additionally, a sample was collected at screening, as well as subsequent visits for evaluation of anti-pegloticase Ab. All lab samples were discarded if the participant is deemed not eligible for the study.

Week −4

Confirm study eligibility through review of the inclusion/exclusion criteria.

Collect medical/surgical history, substance use history, and medication history.

Perform a targeted physical examination included heart, lungs and abdominal exam and joint and skin evaluation and assessment of AEs. Any finding was recorded as an AE.

Document gout flares and intensity.

Record vital signs (blood pressure, respiratory rate, temperature, and heart rate).

Obtain blood samples for hematology and clinical chemistry analysis.

Obtain a urine sample for uric acid:creatinine ratio.

Obtain a urine sample from all females of childbearing potential for performance of a pregnancy test.

Obtain a blood sample for measurement of SUA (only 1 sample for central laboratory).

Collect swollen/tender joint counts; administer HAQ; and record patient and physician global assessments and joint pain assessment responses.

Provide dosing calendar for subjects to record the date and time they take MTX (Additional calendar pages may be provided at future visits as needed).

Dispense MTX.

Fill gout prophylaxis, fexofenadine, acetaminophen, and folic acid prescriptions, as needed.

Inquire about AEs.

Screen failure subjects that take MTX during Week −4 or Week −3, and who were females of childbearing potential, received a safety follow-up phone call/e-mail/site visit approximately 30 days after the last dose of MTX to verify at least one ovulatory cycle had occurred since the last dose of MTX. If the subject had not ovulated, a urine pregnancy test was performed. Screen failure subjects who were non-vasectomized males, a phone/e-mail/site visit inquiry was conducted 3 months after MTX discontinuation regarding partner pregnancy.

Week −2

Confirm study eligibility through review of the inclusion/exclusion criteria.

Obtain blood samples for hematology and clinical chemistry analysis.

Obtain a urine sample for uric acid:creatinine ratio.

Obtain a urine sample from all females of childbearing potential for performance of a pregnancy test.

Obtain a blood sample for measurement of SUA (only 1 sample for central laboratory).

Assess MTX compliance and re-dispense MTX.

Document gout flares and intensity.

Ask Yes/No question regarding folic acid and gout flare prophylaxis compliance.

Fill gout prophylaxis, fexofenadine, acetaminophen, and folic acid prescriptions, as needed.

Collect substance use history, and medication history.

Inquire about AEs.

Screen failure subjects that taken MTX during Week −4 or Week −3, Week −2 or Week −1, and who were females of childbearing potential, received a safety follow-up phone call/e-mail/site visit approximately 30 days after the last dose of MTX to verify at least one ovulatory cycle had occurred since the last dose of MTX. If the subject had not ovulated, a urine pregnancy test was performed. Screen failure subjects who were non-vasectomized males, a phone/e-mail/site visit inquiry was conducted 3 months after MTX discontinuation regarding partner pregnancy.

KXX+IMM Period

Day 1

On Day 1, subjects returned to the clinic for the following assessments and the first dose of pegloticase.

Obtained 1 blood sample for measurement of SUA prior to the pegloticase infusion.

Confirmed study eligibility through review of the inclusion/exclusion criteria.

Administered MTX ≥60 minutes prior to pegloticase infusion if subject had not taken MTX within the previous 1 to 3 days.

Performed a targeted physical examination including heart, lungs and abdominal exam and joint and skin evaluation and assessment of AEs. Any finding was recorded as an AE.

Documented gout flares and intensity.

Recorded vital signs (blood pressure [prior and post infusion], respiratory rate, temperature, and heart rate [prior and post infusion]), including measurement of weight prior to infusion.

Performed 12-lead ECG prior to the pegloticase infusion.

Collected swollen/tender joint counts; administer HAQ; and record patient and physician global assessments and joint pain assessment responses.

Assessed MTX compliance and re-dispense MTX.

Ask Yes/No question regarding folic acid, gout flare prophylaxis, and IR prophylaxis compliance.

Filled gout prophylaxis, fexofenadine, acetaminophen, and folic acid prescriptions, as needed.

Obtained blood samples for hematology and clinical chemistry analysis.

Obtained a urine sample for uric acid:creatinine ratio.

Obtained a urine sample from all females of childbearing potential for performance of a pregnancy test.

Obtained blood samples for MTX Polyglutamate analysis prior to the infusion.

Obtained blood samples for anti-PEG and anti-uricase IgG antibodies prior to the infusion.

Obtained blood samples for pegloticase PK analysis prior to the infusion.

Administered IR prophylaxis (i.e., fexofenadine, acetaminophen, and methylprednisolone or hydrocortisone).

Administered the first dose of pegloticase and record date, volume, and duration of infusion, and start/stop (inclusive of 10-mL flush) times of dosing.

Obtained a blood sample (1 sample) for measurement of SUA after the end of the pegloticase infusion prior to discharge.

Obtained blood samples for pegloticase PK analysis after the end of the infusion prior to discharge.

Inquired about AEs and concomitant medication use.

Performed DECT (if applicable).

Week 1 (Non-infusion visit for those who consent only)

Inquired about AEs and concomitant medication use.

Obtained blood samples for pegloticase PK analysis.

Obtained blood samples for anti-PEG and anti-uricase IgG antibodies.

Obtained a blood sample (1 sample) for measurement of SUA

Week 2

Obtained 2 blood samples for measurement of SUA within 48 hours prior to this visit's pegloticase infusion. Pre-infusion SUA results were reported by the local or central laboratory prior to pegloticase infusion. If a local laboratory sample was drawn at a center other than the research site (within 48 hours prior to the pegloticase infusion), a sample for the central laboratory was drawn prior to the pegloticase infusion on the day of the visit.

Administer MTX ≥60 minutes prior to pegloticase infusion if subject had not taken MTX within the previous 1 to 3 days.

Document gout flares and intensity.

Record vital signs (blood pressure [prior and post infusion], respiratory rate, temperature, and heart rate [prior and post infusion]).

Assess MTX compliance and re-dispense MTX.

Ask Yes/No question regarding folic acid, gout flare prophylaxis, and IR prophylaxis compliance. Fill gout prophylaxis, fexofenadine, acetaminophen, and folic acid prescriptions, as needed.

Obtain blood samples for hematology and clinical chemistry analysis.

Obtain a urine sample for uric acid:creatinine ratio.

Obtain a urine sample from all females of childbearing potential for performance of a pregnancy test.

Obtain blood samples for pegloticase PK analysis prior to the infusion.

Obtain blood samples for anti-PEG and anti-uricase IgG antibodies prior to the infusion.

Administer IR prophylaxis (i.e., fexofenadine, acetaminophen, and methylprednisolone or hydrocortisone).

Administer pegloticase and record date, volume, and duration of infusion, and start/stop (inclusive of 10-mL flush) times of dosing.

Obtain a blood sample (1 sample) for measurement of SUA after the end of pegloticase infusion prior to discharge.

Obtain blood samples for pegloticase PK analysis after the end of the infusion prior to discharge.

Inquire about AEs and concomitant medication use.

Week 4

Obtain 2 blood samples for measurement of SUA within 48 hours prior to this visit's pegloticase infusion. Pre-infusion SUA results were reported by the local or central laboratory prior to pegloticase infusion. If a local laboratory sample was drawn at a center other than the research site (within 48 hours prior to the pegloticase infusion), a sample for the central laboratory was drawn prior to the pegloticase infusion on the day of the visit.

Stopping Rule: Subjects with an SUA level >6 mg/dL at 2 consecutive study visits beginning with the Week 2 Visit (not including post-infusion samples) discontinued treatment and remained in the study.

Administer MTX ≥60 minutes prior to pegloticase infusion if subject had not taken MTX within the previous 1 to 3 days.

Perform a targeted physical examination including heart, lungs and abdominal exam and joint and skin evaluation and assessment of AEs. Any finding was recorded as an AE.

Document gout flares and intensity.

Record vital signs (blood pressure [prior and post infusion], respiratory rate, temperature, and heart rate [prior and post infusion]).

Assess MTX compliance and re-dispense MTX.

Obtain blood samples for MTX Polyglutamate analysis prior to the infusion.

Obtain blood samples for pegloticase PK analysis prior to the infusion.

Obtain blood samples for anti-PEG and anti-uricase IgG antibodies prior to the infusion.

Ask Yes/No question regarding folic acid, gout flare prophylaxis, and IR prophylaxis compliance.

Fill gout prophylaxis, fexofenadine, acetaminophen, and folic acid prescriptions, as needed.

Obtain a urine sample from all females of childbearing potential for performance of a pregnancy test.

Administer IR prophylaxis (i.e., fexofenadine, acetaminophen, and methylprednisolone or hydrocortisone).

Administer pegloticase and record date, volume, and duration of infusion, and start/stop (inclusive of 10-mL flush) times of dosing.

Obtain blood samples for pegloticase PK analysis after the end of the infusion prior to discharge.

Obtain a blood sample (1 sample) for measurement of SUA after the end of pegloticase infusion prior to discharge.

Inquire about AEs and concomitant medication use.

Week 6

Obtain 2 blood samples for measurement of SUA within 48 hours prior to this visit's pegloticase infusion. Pre-infusion SUA results were reported by the local or central laboratory prior to pegloticase infusion. If a local laboratory sample was drawn at a center other than the research site (within 48 hours prior to the pegloticase infusion), a sample for the central laboratory was drawn prior to the pegloticase infusion on the day of the visit.

Stopping Rule: Subjects with an SUA level >6 mg/dL at 2 consecutive study visits beginning with the Week 2 Visit (not including post-infusion samples) discontinued treatment and remained in the study.

Administered MTX >60 minutes prior to pegloticase infusion if subject had not taken MTX within the previous 1 to 3 days.

Documented gout flares and intensity.

Recorded vital signs (blood pressure [prior and post infusion], respiratory rate, temperature, and heart rate [prior and post infusion]).Assess MTX compliance and re-dispense MTX.

Asked Yes/No question regarding folic acid, gout flare prophylaxis, and IR prophylaxis compliance.

Filled gout prophylaxis, fexofenadine, acetaminophen, and folic acid prescriptions, as needed.

Obtained a urine sample from all females of childbearing potential for performance of a pregnancy test.

Obtained blood samples for hematology and clinical chemistry analysis.

Obtained a urine sample for uric acid:creatinine ratio.

Obtained blood samples for pegloticase PK analysis prior to the infusion.

Obtained blood samples for anti-PEG and anti-uricase IgG antibodies prior to the infusion.

Administered IR prophylaxis (i.e., fexofenadine, acetaminophen, and methylprednisolone or hydrocortisone).

Administered pegloticase and record date, volume, and duration of infusion, and start/stop (inclusive of 10-mL flush) times of dosing.

Obtained a blood sample (1 sample) for measurement of SUA after the end of pegloticase infusion prior to discharge.

Obtain blood samples for pegloticase PK analysis after the end of the infusion prior to discharge.

Inquire about AEs and concomitant medication use.

Week 7 (Non-infusion visit for those who consent only)

Inquire about AEs and concomitant medication use.

Obtain blood samples for pegloticase PK analysis

Obtain blood samples for anti-PEG and anti-uricase IgG antibodies prior to the infusion.

Obtain a blood sample (1 sample) for measurement of SUA

Week 8

Obtain 2 blood samples for measurement of SUA within 48 hours prior to this visit's pegloticase infusion. Pre-infusion SUA results were reported by the local or central laboratory prior to pegloticase infusion. If a local laboratory sample was drawn at a center other than the research site (within 48 hours prior to the pegloticase infusion), a sample for the central laboratory was drawn prior to the pegloticase infusion on the day of the visit.

Stopping Rule: Subjects with an SUA level >6 mg/dL at 2 consecutive study visits beginning with the Week 2 Visit (not including post-infusion samples) discontinued treatment and remained in the study.

Administered MTX ≥60 minutes prior to pegloticase infusion if subject had not taken MTX within the previous 1 to 3 days.

Performed a targeted physical examination should include heart, lungs and abdominal exam and joint and skin evaluation and assessment of AEs. Any finding was recorded as an AE.

Documented gout flares and intensity.

Recorded vital signs (blood pressure [prior and post infusion], respiratory rate, temperature, and heart rate [prior and post infusion]), including measurement of weight prior to infusion.

Assessed MTX compliance and re-dispense MTX.

Asked Yes/No question regarding folic acid, gout flare prophylaxis, and IR prophylaxis compliance.

Filled gout prophylaxis, fexofenadine, acetaminophen, and folic acid prescriptions, as needed.

Obtain blood samples for MTX Polyglutamate analysis prior to the infusion.

Obtain blood samples for pegloticase PK analysis prior to the infusion.

Obtain blood samples for anti-PEG and anti-uricase IgG antibodies prior to the infusion.

Obtain a urine sample from all females of childbearing potential for performance of a pregnancy test.

Administer IR prophylaxis (i.e., fexofenadine, acetaminophen, and methylprednisolone or hydrocortisone).

Administer pegloticase and record date, volume, and duration of infusion, and start/stop (inclusive of 10-mL flush) times of dosing.

Obtain a blood sample (1 sample) for measurement of SUA after the end of pegloticase infusion prior to discharge.

Obtain blood samples for pegloticase PK analysis after the end of the infusion prior to discharge.

Inquire about AEs and concomitant medication use.

Week 10

Obtain 2 blood samples for measurement of SUA within 48 hours prior to this visit's pegloticase infusion. Pre-infusion SUA results were reported by the local or central laboratory prior to pegloticase infusion. If a local laboratory sample was drawn at a center other than the research site (within 48 hours prior to the pegloticase infusion), a sample for the central laboratory was drawn prior to the pegloticase infusion on the day of the visit.

Stopping Rule: Subjects with an SUA level >6 mg/dL at 2 consecutive study visits beginning with the Week 2 Visit (not including post-infusion samples) discontinued treatment and remained in the study.

Administered MTX >60 minutes prior to pegloticase infusion if subject had not taken MTX within the previous 1 to 3 days.

Documented gout flares and intensity.

Recorded vital signs (blood pressure [prior and post infusion], respiratory rate, temperature, and heart rate [prior and post infusion]).

Assessed MTX compliance and re-dispense MTX.

Asked Yes/No question regarding folic acid, gout flare prophylaxis, and IR prophylaxis compliance.

Filled gout prophylaxis, fexofenadine, acetaminophen, and folic acid prescriptions, as needed.

Obtained blood samples for pegloticase PK analysis prior to the infusion.

Obtained blood samples for anti-PEG and anti-uricase IgG antibodies prior to the infusion.

Obtained a urine sample from all females of childbearing potential for performance of a pregnancy test.

Administered IR prophylaxis (i.e., fexofenadine, acetaminophen, and methylprednisolone or hydrocortisone).

Administered pegloticase and record date, volume, and duration of infusion, and start/stop (inclusive of 10-mL flush) times of dosing.

Obtained a blood sample (1 sample) for measurement of SUA after the end of pegloticase infusion prior to discharge.

Inquired about AEs and concomitant medication use.

Week 12

Obtained 2 blood samples for measurement of SUA within 48 hours prior to this visit's pegloticase infusion. Pre-infusion SUA results were reported by the local or central laboratory prior to pegloticase infusion. If a local laboratory sample was drawn at a center other than the research site (within 48 hours prior to the pegloticase infusion), a sample for the central laboratory was drawn prior to the pegloticase infusion on the day of the visit.

Stopping Rule: Subjects with an SUA level >6 mg/dL at 2 consecutive study visits beginning with the Week 2 Visit (not including post-infusion samples) discontinued treatment and remained in the study.

Administered MTX >60 minutes prior to pegloticase infusion if subject had not taken MTX within the previous 1 to 3 days.

Performed a targeted physical examination should include heart, lungs and abdominal exam and joint and skin evaluation and assessment of AEs. Any finding was recorded as an AE.

Documented gout flares and intensity.

Recorded vital signs (blood pressure [prior and post infusion], respiratory rate, temperature, and heart rate [prior and post infusion]).

Assessed MTX compliance and re-dispense MTX.

Asked Yes/No question regarding folic acid, gout flare prophylaxis, and IR prophylaxis compliance.

Filled gout prophylaxis, fexofenadine, acetaminophen, and folic acid prescriptions, as needed.

Obtained a urine sample from all females of childbearing potential for performance of a pregnancy test.

Administered IR prophylaxis (i.e., fexofenadine, acetaminophen, and methylprednisolone or hydrocortisone)

Administered pegloticase and record date, volume, and duration of infusion, and start/stop (inclusive of 10-mL flush) times of dosing.

Obtained a blood sample (1 sample) for measurement of SUA after the end of pegloticase infusion prior to discharge.

Inquired about AEs and concomitant medication use.

Week 14

Obtain 2 blood samples for measurement of SUA within 48 hours prior to this visit's pegloticase infusion. Pre-infusion SUA results were reported by the local or central laboratory prior to pegloticase infusion. If a local laboratory sample was drawn at a center other than the research site (within 48 hours prior to the pegloticase infusion), a sample for the central laboratory was drawn prior to the pegloticase infusion on the day of the visit.

Stopping Rule: Subjects with an SUA level >6 mg/dL at 2 consecutive study visits beginning with the Week 2 Visit (not including post-infusion samples) discontinued treatment and remained in the study.

Administered MTX ≥60 minutes prior to pegloticase infusion if subject had not taken MTX within the previous 1 to 3 days.

Documented gout flares and intensity.

Recorded vital signs (blood pressure [prior and post infusion], respiratory rate, temperature, and heart rate [prior and post infusion]).

Collected swollen/tender joint counts; administer HAQ; and record patient and physician global assessments and joint pain assessment responses.

Assessed MTX compliance and re-dispense MTX.

Asked Yes/No question regarding folic acid, gout flare prophylaxis, and IR prophylaxis compliance.

Filled gout prophylaxis, fexofenadine, acetaminophen, and folic acid prescriptions, as needed.

Obtained a urine sample from all females of childbearing potential for performance of a pregnancy test.

Obtained blood samples for hematology and clinical chemistry analysis.

Obtained a urine sample for uric acid:creatinine ratio.

Obtained a blood sample for pegloticase PK analysis prior to the infusion.

Obtained a blood sample for MTX Polyglutamate analysis prior to the infusion.

Obtained blood samples for anti-PEG and anti-uricase IgG antibodies prior to the infusion.

Administered IR prophylaxis (i.e., fexofenadine, acetaminophen, and methylprednisolone or hydrocortisone. Administer pegloticase and record date, volume, and duration of infusion, and start/stop (inclusive of 10-mL flush) times of dosing.

Obtained a blood sample (1 sample) for measurement of SUA after the end of pegloticase infusion prior to discharge.

Inquired about AEs and concomitant medication use.

Week 16

Obtain 2 blood samples for measurement of SUA within 48 hours prior to this visit's pegloticase infusion. Pre-infusion SUA results were reported by the local or central laboratory prior to pegloticase infusion. If a local laboratory sample was drawn at a center other than the research site (within 48 hours prior to the pegloticase infusion), a sample for the central laboratory was drawn prior to the pegloticase infusion on the day of the visit.

Stopping Rule: Subjects with an SUA level >6 mg/dL at 2 consecutive study visits beginning with the Week 2 Visit (not including post-infusion samples) discontinued treatment and remained in the study.

Administered MTX ≥60 minutes prior to pegloticase infusion if subject had not taken MTX within the previous 1 to 3 days.

Performed a targeted physical examination should include heart, lungs and abdominal exam and joint and skin evaluation and assessment of AEs. Any finding was recorded as an AE.

Documented gout flares and intensity.

Recorded vital signs (blood pressure [prior and post infusion], respiratory rate, temperature, and heart rate [prior and post infusion]) including measurement of weight prior to infusion. Assessed MTX compliance and re-dispense MTX.

Asked Yes/No question regarding folic acid, gout flare prophylaxis, and IR prophylaxis compliance.

Filled gout prophylaxis, fexofenadine, acetaminophen, and folic acid prescriptions, as needed.

Obtained a urine sample from all females of childbearing potential for performance of a pregnancy test.

Administered IR prophylaxis (i.e., fexofenadine, acetaminophen, and methylprednisolone or hydrocortisone).

Administer pegloticase and record date, volume, and duration of infusion, and start/stop (inclusive of 10-mL flush) times of dosing.

Obtain a blood sample (1 sample) for measurement of SUA after the end of pegloticase infusion prior to discharge.

Inquire about AEs and concomitant medication use.

Week 18

Obtain 2 blood samples for measurement of SUA within 48 hours prior to this visit's pegloticase infusion. Pre-infusion SUA results were reported by the local or central laboratory prior to pegloticase infusion. If a local laboratory sample was drawn at a center other than the research site (within 48 hours prior to the pegloticase infusion), a sample for the central laboratory was drawn prior to the pegloticase infusion on the day of the visit.

Stopping Rule: Subjects with an SUA level >6 mg/dL at 2 consecutive study visits beginning with the Week 2 Visit (not including post-infusion samples) discontinued treatment and remained in the study.

Administered MTX >60 minutes prior to pegloticase infusion if subject had not taken MTX within the previous 1 to 3 days.

Documented gout flares and intensity.

Recorded vital signs (blood pressure [prior and post infusion], respiratory rate, temperature, and heart rate [prior and post infusion]).Assess MTX compliance and re-dispense MTX.

Asked Yes/No question regarding folic acid, gout flare prophylaxis, and IR prophylaxis compliance.

Filled gout prophylaxis, fexofenadine, acetaminophen, and folic acid prescriptions, as needed.

Obtain aed urine sample from all females of childbearing potential for performance of a pregnancy test.

Obtained blood samples for pegloticase PK analysis prior to the infusion.

Obtained blood samples for anti-PEG and anti-uricase IgG antibodies prior to the infusion.

Administered IR prophylaxis (i.e., fexofenadine, acetaminophen, and methylprednisolone or hydrocortisone).

Administered pegloticase and record date, volume, and duration of infusion, and start/stop (inclusive of 10-mL flush) times of dosing.

Obtained a blood sample (1 sample) for measurement of SUA after the end of pegloticase infusion prior to discharge.

Inquired about AEs and concomitant medication use.

Week 20

Obtained 2 blood samples for measurement of SUA within 48 hours prior to this visit's pegloticase infusion. Pre-infusion SUA results were reported by the local or central laboratory prior to pegloticase infusion. If a local laboratory sample was drawn at a center other than the research site (within 48 hours prior to the pegloticase infusion), a sample for the central laboratory was drawn prior to the pegloticase infusion on the day of the visit.

Stopping Rule: Subjects with an SUA level >6 mg/dL at 2 consecutive study visits beginning with the Week 2 Visit (not including post-infusion samples) discontinude treatment and remained in the study.

Administered MTX ≥60 minutes prior to pegloticase infusion if subject had not taken MTX within the previous 1 to 3 days.

Performed a targeted physical examination should include heart, lungs and abdominal exam and joint and skin evaluation and assessment of AEs. Any finding was recorded as an AE.

Documented gout flares and intensity.

Recorded vital signs (blood pressure [prior and post infusion], respiratory rate, temperature, and heart rate [prior and post infusion]).

Assessed MTX compliance and re-dispense MTX.

Asked Yes/No question regarding folic acid, gout flare prophylaxis, and IR prophylaxis compliance.

Filled gout prophylaxis, fexofenadine, acetaminophen, and folic acid prescriptions, as needed.

Obtained a urine sample from all females of childbearing potential for performance of a pregnancy test.

Administered IR prophylaxis (i.e., fexofenadine, acetaminophen, and methylprednisolone or hydrocortisone).Administer pegloticase and record date, volume, and duration of infusion, and start/stop (inclusive of 10-mL flush) times of dosing.

Obtained a blood sample (1 sample) for measurement of SUA after the end of pegloticase infusion prior to discharge.

Inquired about AEs and concomitant medication use.

Week 22

Obtain 2 blood samples for measurement of SUA within 48 hours prior to this visit's pegloticase infusion. Pre-infusion SUA results were reported by the local or central laboratory prior to pegloticase infusion. If a local laboratory sample was drawn at a center other than the research site (within 48 hours prior to the pegloticase infusion), a sample for the central laboratory was drawn prior to the pegloticase infusion on the day of the visit.

Stopping Rule: Subjects with an SUA level >6 mg/dL at 2 consecutive study visits beginning with the Week 2 Visit (not including post-infusion samples) discontinued treatment and remained in the study.

Administered MTX ≥60 minutes prior to pegloticase infusion if subject had not taken MTX within the previous 1 to 3 days.

Documented gout flares and intensity.

Recorded vital signs (blood pressure [prior and post infusion], respiratory rate, temperature, and heart rate [prior and post infusion]).

Assessed MTX compliance and re-dispense MTX.

Asked Yes/No question regarding folic acid, gout flare prophylaxis, and IR prophylaxis compliance.

Week 24

Obtained 2 blood samples for measurement of SUA within 48 hours prior to this visit's pegloticase infusion. Pre-infusion SUA results were reported by the local or central laboratory prior to pegloticase infusion. If a local laboratory sample was drawn at a center other than the research site (within 48 hours prior to the pegloticase infusion), a sample for the central laboratory was drawn prior to the pegloticase infusion on the day of the visit.

Stopping Rule: Subjects with an SUA level >6 mg/dL at 2 consecutive study visits beginning with the Week 2 Visit (not including post-infusion samples) discontinued treatment and remaiedn in the study.

Administered MTX ≥60 minutes prior to pegloticase infusion if subject had not taken MTX within the previous 1 to 3 days.

Performed a targeted physical examination should include heart, lungs and abdominal exam and joint and skin evaluation and assessment of AEs. Any finding was recorded as an AE.

Documented gout flares and intensity.

Recorded vital signs (blood pressure [prior and post infusion], respiratory rate, temperature, and heart rate [prior and post infusion]), including measurement of weight prior to infusion. Collected swollen/tender joint counts; administer HAQ; and record patient and physician global assessments and joint pain assessment responses. Assess for the presence of tophi.

Assessed MTX compliance and re-dispense MTX.

Asked Yes/No question regarding folic acid, gout flare prophylaxis, and IR prophylaxis compliance.

Filled gout prophylaxis, fexofenadine, acetaminophen, and folic acid prescriptions, as needed.

Obtained blood samples for hematology and clinical chemistry analysis.

Obtained a urine sample for uric acid:creatinine ratio.

Obtained a urine sample from all females of childbearing potential for performance of a pregnancy test.

Obtained blood samples for MTX Polyglutamate analysis prior to the infusion.

Obtained blood samples for pegloticase PK analysis prior to the infusion.

Obtained blood samples for anti-PEG and anti-uricase IgG antibodies prior to the infusion.

Administered IR prophylaxis (i.e., fexofenadine, acetaminophen, and methylprednisolone or hydrocortisone).

Administered the first dose of pegloticase and record date, volume, and duration of infusion, and start/stop (inclusive of 10-mL flush) times of dosing.

Obtained a blood sample (1 sample) for measurement of SUA after the end of pegloticase infusion prior to discharge.

Inquired about AEs and concomitant medication use.

Performed DECT (if applicable).

Performed Investigator assessment of Clinical Status.

Week 26

Obtain 2 blood samples for measurement of SUA within 48 hours prior to this visit's pegloticase infusion. Pre-infusion SUA results were reported by the local or central laboratory prior to pegloticase infusion. If a local laboratory sample was drawn at a center other than the research site (within 48 hours prior to the pegloticase infusion), a sample for the central laboratory was drawn prior to the pegloticase infusion on the day of the visit.

Stopping Rule: Subjects with an SUA level >6 mg/dL at 2 consecutive study visits beginning with the Week 2 Visit (not including post-infusion samples) discontinued treatment and remained in the study.

Administered MTX ≥60 minutes prior to pegloticase infusion if subject had not taken MTX within the previous 1 to 3 days.

Documented gout flares and intensity.

Recorded vital signs (blood pressure [prior and post infusion], respiratory rate, temperature, and heart rate [prior and post infusion]).Assess MTX compliance and re-dispense MTX.

Asked Yes/No question regarding folic acid, gout flare prophylaxis, and IR prophylaxis compliance.

Filled gout prophylaxis, fexofenadine, acetaminophen, and folic acid prescriptions, as needed.

Obtained a urine sample from all females of childbearing potential for performance of a pregnancy test.

Administered IR prophylaxis (i.e., fexofenadine, acetaminophen, and methylprednisolone or hydrocortisone).

Administered pegloticase and record date, volume, and duration of infusion, and start/stop (inclusive of 10-mL flush) times of dosing.

Inquired about AEs and concomitant medication use.

Week 28

Obtained 2 blood samples for measurement of SUA within 48 hours prior to this visit's pegloticase infusion. Pre-infusion SUA results were reported by the local or central laboratory prior to pegloticase infusion. If a local laboratory sample was drawn at a center other than the research site (within 48 hours prior to the pegloticase infusion), a sample for the central laboratory was drawn prior to the pegloticase infusion on the day of the visit.

Stopping Rule: Subjects with an SUA level >6 mg/dL at 2 consecutive study visits beginning with the Week 2 Visit (not including post-infusion samples) discontinued treatment and remained in the study.

Administer MTX ≥60 minutes prior to pegloticase infusion if subject had not taken MTX within the previous 1 to 3 days.

Document gout flares and intensity.

Record vital signs (blood pressure [prior and post infusion], respiratory rate, temperature, and heart rate [prior and post infusion]).Assess MTX compliance and re-dispense MTX.

Ask Yes/No question regarding folic acid, gout flare prophylaxis, and IR prophylaxis compliance.

Fill gout prophylaxis, fexofenadine, acetaminophen, and folic acid prescriptions, as needed.

Obtain a urine sample from all females of childbearing potential for performance of a pregnancy test.

Administer IR prophylaxis (i.e., fexofenadine, acetaminophen, and methylprednisolone or hydrocortisone).Administer pegloticase and record date, volume, and duration of infusion, and start/stop (inclusive of 10-mL flush) times of dosing.

Inquire about AEs and concomitant medication use.

Week 30

Obtain 2 blood samples for measurement of SUA within 48 hours prior to this visit's pegloticase infusion. Pre-infusion SUA results were reported by the local or central laboratory prior to pegloticase infusion. If a local laboratory sample was drawn at a center other than the research site (within 48 hours prior to the pegloticase infusion), a sample for the central laboratory was drawn prior to the pegloticase infusion on the day of the visit.

Stopping Rule: Subjects with an SUA level >6 mg/dL at 2 consecutive study visits beginning with the Week 2 Visit (not including post-infusion samples) discontinued treatment and remained in the study.

Administered MTX ≥60 minutes prior to pegloticase infusion if subject had not taken MTX within the previous 1 to 3 days.

Documented gout flares and intensity.

Recorded vital signs (blood pressure [prior and post infusion], respiratory rate, temperature, and heart rate [prior and post infusion]).Assess MTX compliance and re-dispense MTX.

Asked Yes/No question regarding folic acid, gout flare prophylaxis, and IR prophylaxis compliance.

Filled gout prophylaxis, fexofenadine, acetaminophen, and folic acid prescriptions, as needed.

Obtained a urine sample from all females of childbearing potential for performance of a pregnancy test.

Administered IR prophylaxis (i.e., fexofenadine, acetaminophen, and methylprednisolone or hydrocortisone). Administered pegloticase and record date, volume, and duration of infusion, and start/stop (inclusive of 10-mL flush) times of dosing.

Inquired about AEs and concomitant medication use.

Week 32

Obtained 2 blood samples for measurement of SUA within 48 hours prior to this visit's pegloticase infusion. Pre-infusion SUA results were reported by the local or central laboratory prior to pegloticase infusion. If a local laboratory sample was drawn at a center other than the research site (within 48 hours prior to the pegloticase infusion), a sample for the central laboratory was drawn prior to the pegloticase infusion on the day of the visit. Stopping Rule: Subjects with an SUA level >6 mg/dL at 2 consecutive study visits beginning with the Week 2 Visit (not including post-infusion samples) discontinued treatment and remained in the study.

Administered MTX >60 minutes prior to pegloticase infusion if subject had not taken MTX within the previous 1 to 3 days.

Documented gout flares and intensity.

Recorded vital signs (blood pressure [prior and post infusion], respiratory rate, temperature, and heart rate [prior and post infusion]).Assess MTX compliance and re-dispense MTX.

Asked Yes/No question regarding folic acid, gout flare prophylaxis, and IR prophylaxis compliance.

Filled gout prophylaxis, fexofenadine, acetaminophen, and folic acid prescriptions, as needed.

Obtained a urine sample from all females of childbearing potential for performance of a pregnancy test.

Administer IR prophylaxis (i.e., fexofenadine, acetaminophen, and methylprednisolone or hydrocortisone).Administer pegloticase and record date, volume, and duration of infusion, and start/stop (inclusive of 10-mL flush) times of dosing.

Obtain a blood sample (1 sample) for measurement of SUA after the end of pegloticase infusion prior to discharge.

Inquire about AEs and concomitant medication use.

Week 34

Obtain 2 blood samples for measurement of SUA within 48 hours prior to this visit's pegloticase infusion. Pre-infusion SUA results were reported by the local or central laboratory prior to pegloticase infusion. If a local laboratory sample was drawn at a center other than the research site (within 48 hours prior to the pegloticase infusion), a sample for the central laboratory was drawn prior to the pegloticase infusion on the day of the visit. Stopping Rule: Subjects with an SUA level >6 mg/dL at 2 consecutive study visits beginning with the Week 2 Visit (not including post-infusion samples) discontinued treatment and remained in the study.

Administered MTX ≥60 minutes prior to pegloticase infusion if subject had not taken MTX within the previous 1 to 3 days.

Documented gout flares and intensity.

Recorded vital signs (blood pressure [prior and post infusion], respiratory rate, temperature, and heart rate [prior and post infusion]). Assess MTX compliance and re-dispense MTX.

Asked Yes/No question regarding folic acid, gout flare prophylaxis, and IR prophylaxis compliance.

Filled gout prophylaxis, fexofenadine, acetaminophen, and folic acid prescriptions, as needed.

Obtained a urine sample from all females of childbearing potential for performance of a pregnancy test.

Administered IR prophylaxis (i.e., fexofenadine, acetaminophen, and methylprednisolone or hydrocortisone), administer pegloticase and record date, volume, and duration of infusion, and start/stop (inclusive of 10-mL flush) times of dosing.

Obtained a blood sample (1 sample) for measurement of SUA after the end of pegloticase infusion prior to discharge.

Inquire about AEs and concomitant medication use.

Week 36

Obtain 2 blood samples for measurement of SUA within 48 hours prior to this visit's pegloticase infusion. Pre-infusion SUA results were reported by the local or central laboratory prior to pegloticase infusion. If a local laboratory sample was drawn at a center other than the research site (within 48 hours prior to the pegloticase infusion), a sample for the central laboratory was drawn prior to the pegloticase infusion on the day of the visit. Stopping Rule: Subjects with an SUA level >6 mg/dL at 2 consecutive study visits beginning with the Week 2 Visit (not including post-infusion samples) discontinued treatment and remained in the study.

Administer MTX ≥60 minutes prior to pegloticase infusion if subject had not taken MTX within the previous 1 to 3 days.

Document gout flares and intensity.

Perform a targeted physical examination including heart, lungs and abdominal exam and joint and skin evaluation and assessment of AEs. Any finding was recorded as an AE.

Record vital signs (blood pressure [prior and post infusion], respiratory rate, temperature, and heart rate [prior and post infusion]) including measurement of weight.

Collect swollen/tender joint counts; administer HAQ; and record patient and physician global assessments and joint pain assessment responses.

Assess for the presence of tophi.

Assess MTX compliance and re-dispense MTX.

Ask Yes/No question regarding folic acid, gout flare prophylaxis, and IR prophylaxis compliance.

Fill gout prophylaxis, fexofenadine, acetaminophen, and folic acid prescriptions, as needed.

Obtain a urine sample from all females of childbearing potential for performance of a pregnancy test.

Obtain blood samples for hematology and clinical chemistry analysis.

Obtain a urine sample for uric acid:creatinine ratio.

Obtain blood samples for pegloticase PK analysis prior to the infusion.

Obtain blood samples for anti-PEG and anti-uricase IgG antibodies prior to the infusion.

Obtain blood samples for MTX Polyglutamate analysis prior to the infusion.

Administer IR prophylaxis (i.e., fexofenadine, acetaminophen, and methylprednisolone or hydrocortisone), administer pegloticase and record date, volume, and duration of infusion, and start/stop (inclusive of 10-mL flush) times of dosing.

Obtain a blood sample (1 sample) for measurement of SUA after the end of pegloticase infusion prior to discharge.

Obtain blood samples for pegloticase PK analysis after the end of the infusion prior to discharge.

Perform DECT (if applicable).

Inquire about AEs and concomitant medication use.

Week 38

Obtain 2 blood samples for measurement of SUA within 48 hours prior to this visit's pegloticase infusion. Pre-infusion SUA results were reported by the local or central laboratory prior to pegloticase infusion. If a local laboratory sample was drawn at a center other than the research site (within 48 hours prior to the pegloticase infusion), a sample for the central laboratory was drawn prior to the pegloticase infusion on the day of the visit. Stopping Rule: Subjects with an SUA level >6 mg/dL at 2 consecutive study visits beginning with the Week 2 Visit (not including post-infusion samples) discontinued treatment and remained in the study.

Administer MTX ≥60 minutes prior to pegloticase infusion if subject had not taken MTX within the previous 1 to 3 days.

Document gout flares and intensity.

Record vital signs (blood pressure [prior and post infusion], respiratory rate, temperature, and heart rate [prior and post infusion]).

Assess MTX compliance and re-dispense MTX.

Ask Yes/No question regarding folic acid, gout flare prophylaxis, and IR prophylaxis compliance.

Fill gout prophylaxis, fexofenadine, acetaminophen, and folic acid prescriptions, as needed.

Obtain a urine sample from all females of childbearing potential for performance of a pregnancy test.

Administer IR prophylaxis (i.e., fexofenadine, acetaminophen, and methylprednisolone or hydrocortisone), administer pegloticase and record date, volume, and duration of infusion, and start/stop (inclusive of 10-mL flush) times of dosing. Inquire about AEs and concomitant medication use.

Week 40

Obtain 2 blood samples for measurement of SUA within 48 hours prior to this visit's pegloticase infusion. Pre-infusion SUA results were reported by the local or central laboratory prior to pegloticase infusion. If a local laboratory sample was drawn at a center other than the research site (within 48 hours prior to the pegloticase infusion), a sample for the central laboratory was drawn prior to the pegloticase infusion on the day of the visit. Stopping Rule: Subjects with an SUA level >6 mg/dL at 2 consecutive study visits beginning with the Week 2 Visit (not including post-infusion samples) discontinued treatment and remained in the study.

Administer edMTX ≥60 minutes prior to pegloticase infusion if subject had not taken MTX within the previous 1 to 3 days.

Documented gout flares and intensity.

Recorded vital signs (blood pressure [prior and post infusion], respiratory rate, temperature, and heart rate [prior and post infusion]).Assess MTX compliance and re-dispense MTX.

Asked Yes/No question regarding folic acid, gout flare prophylaxis, and IR prophylaxis compliance.

Filled gout prophylaxis, fexofenadine, acetaminophen, and folic acid prescriptions, as needed.

Obtained a urine sample from all females of childbearing potential for performance of a pregnancy test.

Administered IR prophylaxis (i.e., fexofenadine, acetaminophen, and methylprednisolone or hydrocortisone). Administered pegloticase and record date, volume, and duration of infusion, and start/stop (inclusive of 10-mL flush) times of dosing.

Inquired about AEs and concomitant medication use.

Week 42

Obtain 2 blood samples for measurement of SUA within 48 hours prior to this visit's pegloticase infusion. Pre-infusion SUA results were reported by the local or central laboratory prior to pegloticase infusion. If a local laboratory sample was drawn at a center other than the research site (within 48 hours prior to the pegloticase infusion), a sample for the central laboratory was drawn prior to the pegloticase infusion on the day of the visit. Stopping Rule: Subjects with an SUA level >6 mg/dL at 2 consecutive study visits beginning with the Week 2 Visit (not including post-infusion samples) discontinued treatment and remained in the study.

Administered MTX ≥60 minutes prior to pegloticase infusion if subject had not taken MTX within the previous 1 to 3 days.

Documented gout flares and intensity.

Recorded vital signs (blood pressure [prior and post infusion], respiratory rate, temperature, and heart rate [prior and post infusion]). Assessed MTX compliance and re-dispense MTX.

Asked Yes/No question regarding folic acid, gout flare prophylaxis, and IR prophylaxis compliance.

Filled gout prophylaxis, fexofenadine, acetaminophen, and folic acid prescriptions, as needed.

Obtained a urine sample from all females of childbearing potential for performance of a pregnancy test.

Administered IR prophylaxis (i.e., fexofenadine, acetaminophen, and methylprednisolone or hydrocortisone).

Administered pegloticase and record date, volume, and duration of infusion, and start/stop (inclusive of 10-mL flush) times of dosing.

Inquired about AEs and concomitant medication use.

Week 44

Obtained 2 blood samples for measurement of SUA within 48 hours prior to this visit's pegloticase infusion. Pre-infusion SUA results were reported by the local or central laboratory prior to pegloticase infusion. If a local laboratory sample was drawn at a center other than the research site (within 48 hours prior to the pegloticase infusion), a sample for the central laboratory was drawn prior to the pegloticase infusion on the day of the visit. Stopping Rule: Subjects with an SUA level >6 mg/dL at 2 consecutive study visits beginning with the Week 2 Visit (not including post-infusion samples) discontinued treatment and remained in the study.

Administered MTX ≥60 minutes prior to pegloticase infusion if subject had not taken MTX within the previous 1 to 3 days.

Documented gout flares and intensity.

Recorded vital signs (blood pressure [prior and post infusion], respiratory rate, temperature, and heart rate [prior and post infusion]).

Assessed MTX compliance and re-dispense MTX.

Asked Yes/No question regarding folic acid, gout flare prophylaxis, and IR prophylaxis compliance.

Filled gout prophylaxis, fexofenadine, acetaminophen, and folic acid prescriptions, as needed.

Obtained a urine sample from all females of childbearing potential for performance of a pregnancy test.

Administered IR prophylaxis (i.e., fexofenadine, acetaminophen, and methylprednisolone or hydrocortisone). Administered pegloticase and record date, volume, and duration of infusion, and start/stop (inclusive of 10-mL flush) times of dosing.

Inquired about AEs and concomitant medication use.

Week 46

Obtained 2 blood samples for measurement of SUA within 48 hours prior to this visit's pegloticase infusion. Pre-infusion SUA results were reported by the local or central laboratory prior to pegloticase infusion. If a local laboratory sample was drawn at a center other than the research site (within 48 hours prior to the pegloticase infusion), a sample for the central laboratory was drawn prior to the pegloticase infusion on the day of the visit. Stopping Rule: Subjects with an SUA level >6 mg/dL at 2 consecutive study visits beginning with the Week 2 Visit (not including post-infusion samples) discontinued treatment and remained in the study.

Administered MTX ≥60 minutes prior to pegloticase infusion if subject had not taken MTX within the previous 1 to 3 days.

Documented gout flares and intensity.

Recorded vital signs (blood pressure [prior and post infusion], respiratory rate, temperature, and heart rate [prior and post infusion]).

Assessed MTX compliance and re-dispense MTX.

Asked Yes/No question regarding folic acid, gout flare prophylaxis, and IR prophylaxis compliance.

Filled gout prophylaxis, fexofenadine, acetaminophen, and folic acid prescriptions, as needed.

Obtained a urine sample from all females of childbearing potential for performance of a pregnancy test.

Administered IR prophylaxis (i.e., fexofenadine, acetaminophen, and methylprednisolone or hydrocortisone). Administered pegloticase and record date, volume, and duration of infusion, and start/stop (inclusive of 10-mL flush) times of dosing.

Inquired about AEs and concomitant medication use.

Week 48

Obtained 2 blood samples for measurement of SUA within 48 hours prior to this visit's pegloticase infusion. Pre-infusion SUA results were reported by the local or central laboratory prior to pegloticase infusion. If a local laboratory sample was drawn at a center other than the research site (within 48 hours prior to the pegloticase infusion), a sample for the central laboratory was drawn prior to the pegloticase infusion on the day of the visit. Stopping Rule: Subjects with an SUA level >6 mg/dL at 2 consecutive study visits beginning with the Week 2 Visit (not including post-infusion samples) discontinued treatment and remained in the study.

Administered MTX ≥60 minutes prior to pegloticase infusion if subject had not taken MTX within the previous 1 to 3 days.

Documented gout flares and intensity.

Recorded vital signs (blood pressure [prior and post infusion], respiratory rate, temperature, and heart rate [prior and post infusion]). Assessed MTX compliance and re-dispense MTX.

Asked Yes/No question regarding folic acid, gout flare prophylaxis, and IR prophylaxis compliance.

Filled gout prophylaxis, fexofenadine, acetaminophen, and folic acid prescriptions, as needed.

Obtained a urine sample from all females of childbearing potential for performance of a pregnancy test.

Administer IR prophylaxis (i.e., fexofenadine, acetaminophen, and methylprednisolone or hydrocortisone).Administer pegloticase and record date, volume, and duration of infusion, and start/stop (inclusive of 10-mL flush) times of dosing.

Obtain a blood sample (1 sample) for measurement of SUA after the end of pegloticase infusion prior to discharge.

Inquire about AEs and concomitant medication use.

Week 50

Obtain 2 blood samples for measurement of SUA within 48 hours prior to this visit's pegloticase infusion. Pre-infusion SUA results were reported by the local or central laboratory prior to pegloticase infusion. If a local laboratory sample was drawn at a center other than the research site (within 48 hours prior to the pegloticase infusion), a sample for the central laboratory was drawn prior to the pegloticase infusion on the day of the visit. Stopping Rule: Subjects with an SUA level >6 mg/dL at 2 consecutive study visits beginning with the Week 2 Visit (not including post-infusion samples) discontinued treatment and remained in the study.

Administered MTX ≥60 minutes prior to pegloticase infusion if subject had not taken MTX within the previous 1 to 3 days.

Documented gout flares and intensity.

Recorded vital signs (blood pressure, one measurement [prior and post infusion], respiratory rate, temperature, and heart rate [prior and post infusion]). Assessed MTX compliance and dispense.

Asked Yes/No question regarding folic acid, gout flare prophylaxis, and IR prophylaxis compliance.

Obtained a urine sample from all females of childbearing potential for performance of a pregnancy test.

Administered IR prophylaxis (i.e., fexofenadine, acetaminophen, and methylprednisolone or hydrocortisone).

Administered pegloticase and record date, volume, and duration of infusion, and start/stop (inclusive of 10-mL flush) times of dosing.

Obtained a blood sample (1 sample) for measurement of SUA after the end of pegloticase infusion prior to discharge.

Inquired about AEs and concomitant medication use.

MTX was taken one week following the Week 50 Visit and Folic Acid was taken until just prior to the Week 52 Visit.

End of Pegloticase Infusions Visit

Subjects who end pegloticase infusions prior to Week 52 completed the End of Pegloticase Infusions Visit procedures following their final infusion. Subjects continued to participate in all visits through the end of the study. Subjects completed selected study visits at the study site during key efficacy and safety collections Weeks 10, 12, 14, 20, 22, 24, 32, 34, 36, 48, 50 and 52, so that SUA labs and other key assessments can be completed. Visits between these key efficacy and safety collection visits, for subjects who stopped infusions, may be completed in person or via a telephone visit option to collect AEs, concomitant medication and gout flare information. The following procedures were completed at the End of Pegloticase Visit:

Investigator Assessment of Clinical Status.

Document gout flares and intensity.

Perform a targeted physical examination including heart, lungs and abdominal exam and joint and skin evaluation and assessment of AEs. Any finding was recorded as an AE.

Record vital signs (blood pressure, respiratory rate, temperature, and heart rate including the measurement of weight. Collect swollen/tender joint counts; administer HAQ; and record patient and physician global assessments and joint pain assessment responses.

Assessment of Tophi.

Assess MTX compliance.

Ask Yes/No question regarding folic acid, gout flare prophylaxis, and IR prophylaxis compliance.

Obtain a urine sample from all females of childbearing potential for performance of a pregnancy test.

Obtain blood samples for hematology and clinical chemistry analysis.

Obtain a urine sample for uric acid:creatinine ratio.

Obtain blood samples for pegloticase PK analysis.

Obtain blood samples for anti-PEG and anti-uricase IgG antibodies.

Obtain a blood sample (1 sample) for measurement of SUA.

Inquire about AEs and concomitant medication use.

Perform DECT (if applicable). DECT may be completed within+/−5 days of the scheduled visit. Subjects who end pegloticase infusions prior to Week 52 should follow the scheduled timepoints but avoid a repeat DECT scan within 6 weeks of a prior scan.

Week 52/End of Study/Early Termination Visit

Investigator Assessment of Clinical Status.

Perform a targeted physical examination including heart, lungs and abdominal exam and joint and skin evaluation and assessment of AEs. Any finding was recorded as an AE.

Assessment of Tophi.

Document gout flares and intensity.

Record vital signs (blood pressure, respiratory rate, temperature, heart rate) and weight measurement. Collect swollen/tender joint counts; administer HAQ; and record patient and physician global assessments and joint pain assessment responses.

Assess MTX compliance.

Ask Yes/No question regarding folic acid, gout flare prophylaxis, and IR prophylaxis compliance.

Obtain a sample from all females of childbearing potential for performance of a pregnancy test.

Obtain blood samples for hematology and clinical chemistry analysis.

Obtain a urine sample for uric acid:creatinine ratio.

Obtain a blood sample (1 sample) for measurement of SUA.

Obtain blood samples for pegloticase PK analysis.

Obtain blood samples for anti-PEG and anti-uricase IgG antibodies.

Inquire about AEs and concomitant medication use.

Perform DECT (if applicable). DECT may be completed within +/−5 days of the scheduled visit.

Safety Follow-Up Phone/Email/Site Visits

Thirty (30) days after the last MTX dose, subjects were contacted by telephone or email or may visit the site to review SAEs. Subjects who were females of childbearing potential were asked to confirm that ovulation had occurred. If the subject had not ovulated, the subject was requested to return to the site for a urine pregnancy test.

Post Treatment Follow-Up

The intent was for at least 6 months of follow-up on each subject after cessation of pegloticase infusions. If these 6 months occur prior to end of study at Week 52, such as in the case of a subject who ends pegloticase infusions on or before Week 24, there were no follow-up visits after the Week 52/End of Study Visit. For subjects who end pegloticase infusions between Weeks 26 and 36, there were at least 3 months of follow-up while the subject remains on-study prior to Week 52, and then one follow-up visit after the Week 52/End of Study Visit. For subjects who end pegloticase infusions between Weeks 38 and 52, there were two follow-up visits at intervals of 3 months apart after the Week 52/End of Study Visit. The following procedures were completed at the 3- and 6-month Post Treatment Follow-up Visits:

Document gout flares and intensity.

Record vital signs (blood pressure, respiratory rate, temperature, heart rate and weight). Perform a targeted physical examination including heart, lungs and abdominal exam and joint and skin evaluation and assessment of AEs. Any finding was recorded as an AE.

Collect swollen/tender joint counts; administer HAQ; and record patient and physician global assessments and joint pain assessment responses.

Assessment of Tophi.

Obtain blood samples for hematology and clinical chemistry analysis. Obtain a blood sample (1 sample) for measurement of SUA. Obtain blood samples for anti-PEG and anti-uricase IgG antibodies prior to the infusion (3 Month Post Treatment Follow-up Visit only),Inquire about AEs and concomitant medication use.

Gout Flare Prophylaxis

It is required that before a subject begins the KXX+MTX Period, he or she had been taking at least one protocol standard gout flare prophylaxis regimen (i.e., colchicine and/or non-steroidal anti-inflammatory drugs and/or low-dose prednisone ≤10 mg/day) for ≥1 week before the first dose of pegloticase and continues flare prophylaxis per American College of Rheumatology guidelines (Khanna et al., 2012) for the greater of (1) 6 months, (2) 3 months after achieving target serum urate (SUA <6 mg/dL) for patients with no tophi detected on physical exam, or (3) 6 months after achieving target serum urate (SUA <5 mg/dL) for patients with one or more tophi detected on initial physical exam that have since resolved. For IR prophylaxis, fexofenadine (60 mg or 180 mg orally based on the Principal Investigator's discretion) was taken the day before each infusion; fexofenadine (60 mg or 180 mg orally based on the Principal Investigator's discretion) and acetaminophen (1000 mg orally) were taken the morning of each infusion; and methylprednisolone (125 mg IV) given over the infusion duration 10-30 minutes (recommended) or hydrocortisone (200 mg IV) was administered immediately prior to each infusion. Gout flare prophylaxis continued for the duration of the study unless medically contraindicated or not tolerated.

Example 6

Medications and Dosing

Pharmacy—MTX 2.5 mg tablets for oral administration were provided to subjects as a commercially available generic. MTX was purchased in bulk quantity. The centralized management of the medication allowed maintenance of a trial. Adherence to the medication was recorded by pill counts at the follow-up study visits and consumption of at least 80% were required to consider the participant compliant. A non-compliant participant continued in the study and entered analyses as mandated by statistician.

Pegloticase—Pegloticase, a clear, colorless, sterile solution in phosphate-buffered saline intended for IV infusion after dilution, were supplied by Horizon Pharma, PLC. Pegloticase is commercially available in the US in a single-use, 2 mL glass vial with a Teflon® coated (latex-free) rubber injection stopper. Each mL of pegloticase contained 8 mg of uricase protein conjugated to 24 mg of 10 kDa monomethoxypoly(ethylene glycol). Excipients included disodium hydrogen phosphate dihydrate, sodium chloride, sodium dihydrogen phosphate dehydrate, and water for injection.

All participants in the study received pegloticase at the same dose of 8 mg administered IV every 2 weeks for a total of 6 infusions over a 12-week treatment period, and over an additional 12-week pegloticase opt-in follow-up period (per standard of care).

Packaging and Clinical Supplies—Study drug pegloticase was provided by Horizon Pharma, PLC.

Storage and Return—Before preparation for use, pegloticase was stored in the carton, maintained under refrigeration between 2° C. and 8° C. (36° F. and 46° F.), protected from light, and was not shaken or frozen. Investigational clinical supplies were received by a designated person at the study site, handled and stored safely and properly, and kept in a secured location to which only the Investigator and designated assistants had access. Clinical supplies were dispensed only in accordance with the protocol. Accurate records were kept of the clinical supplies received, the amount dispensed for each participant, and the amount remaining at conclusion of the study. The label of any vials that were not to be used were marked with a large “X,” and the reason for rejecting them was documented on the drug accountability log. In accordance with good pharmacy practice, gloves were worn during preparation of the dose.

The study sites maintained an inventory of drug supplies received and dispensed. UAB provided forms to document all inventory transactions. Upon completion or termination of the study, all clinical pegloticase supplies (used and unused), were destroyed with written certification confirming destruction within sixty (60) days of study completion or expiration of the study drug.

Preparation—Vials were visually inspected for particulate matter and discoloration before administration, whenever solution and container permit. Vials were not used if either was present. Using appropriate aseptic technique, 1 mL of pegloticase was withdrawn from the vial into a sterile syringe. Any unused portion of product remaining in the vial was discarded. Syringe contents were injected into a single 250 mL bag of 0.45% or 0.9% Sodium Chloride Injection, United States Pharmacopeia (USP) for IV infusion and was not mixed or diluted with other drugs. The infusion bag containing the dilute pegloticase solution was inverted several times, but not shaken, to ensure thorough mixing.

Pegloticase diluted in infusion bags was stable for 4 hours at 2° C. to 8° C. (36° F. to 46° F.) and at room temperature (20° C. to 25° C., 68° F. to 77° F.); however, the diluted solution was stored under refrigeration, not frozen, protected from light, and used within 4 hours of dilution. Before administration, the diluted solution of pegloticase was allowed to reach room temperature. Pegloticase in a vial or IV infusion fluid was never subjected to artificial heating.

Administration—Pegloticase was administered as an admixture of 8 mg in 250 mL of 0.45% or 0.9% Sodium Chloride Injection, USP for IV infusion over a target infusion time of 120 minutes by gravity feed or infusion pump. Pegloticase was not administered as an IV push or bolus. Standardized IR prophylaxis consisting of pre-treatment with antihistamines and corticosteroids accompanied each infusion. The drug name, dose, and timing of these prophylactic medications were recorded.

Participants were not fasting on the day of infusion; they were encouraged to have a snack or normal meal 1 hour before, or immediately after, the infusion. Prior to pegloticase infusion participants received infusion prophylaxis (e.g., oral fexofenadine (60 mg) the night before and fexofenadine (60 mg/PO) and acetaminophen (1000 mg/PO) the morning of the infusion; and hydrocortisone IV (200 mg) immediately prior to the infusion).

In a patent IV site, using tubing with no in-line filter, infuse the drug preparation over approximately 120 minutes (within±15 minutes) while the participant was under close observation for any signs of distress. Administration of drug was immediately discontinued if respiratory distress, agitation, chest or back pain, urticaria, or another clinically significant event occurs during infusion. If the AE meets the definition of an SAE, the infusion may not be restarted under any circumstances. A SAE was reported within 2 hours or sooner to the Data Safety Monitoring Board (DSMB). If the AE does not meet the definition of an SAE, the site PI may make the decision to re-start the infusion depending upon the nature and severity of the AE.

Infusions after an infusion-related reaction in an individual participant may be given in a larger volume of diluent, not to exceed 500 mL. In such a case, the infusion duration was also extended to a minimum of 3 hours. The total volume and duration of infusion was captured in the medical record and CRF.

As a precaution, emergency equipment was readily available to treat a possible hypersensitivity reaction and included drugs that treat an anaphylactic reaction. Personnel fully trained in advanced cardiopulmonary resuscitation and in the use of the emergency equipment was readily available during, and for 1 hour after, the infusion. At the end of the infusion, the IV line was flushed with 10 mL of normal saline to assure the full dose was administered. As IRs can occur after completion observation of participants for approximately an hour post-infusion was performed.

Methotrexate (MTX)—MTX, the immune modulator therapy for the study, is an antifolate drug, and thus inhibits the activation of folic acid in the body. MTX is structurally similar to folic acid, which is important for making new cells. MTX inhibits the enzyme dihydrofolate reductase, which activates folic acid.

Packaging and Clinical Supplies:

Labeling—Blinded study drug labeling was annotated with the protocol number by the research pharmacist at the University of Alabama at Birmingham.

Administration—Patients were instructed on how to take MTX. If a dose was missed, it was administered as soon as it was remembered. If it was close to the next scheduled dose, the participant was instructed to skip the missed dose and resume at the next regularly scheduled time; thus, participants were instructed not to double a dose to make up for a missed dose.

Concomitant Medications—Concomitant medications were defined as drug or biological products other than the study drug(s) taken by a participant during the clinical trial. This includes other prescription medications (including preventive vaccines), over-the-counter medications, herbal medications, vitamins, and food supplements.

A comprehensive list of participant's concomitant medications were collected at baseline and at each visit. This included the name of the drug/vitamin/supplement, dose, route of administration, start and stop dates, and the reason for which the medication was taken. All medications were listed by participant using the generic name(s) of the drug/vitamin/supplement.

Severe/Serious adverse events related to the use of a concomitant drug/vitamin/supplement were documented on the appropriate AE CRF.

Gout Flare Prophylaxis—All participants received prophylactic treatment to reduce the risk of acute gout flares, unless medically contraindicated or not tolerated as noted in the FDA-approved pegloticase full prescribing information. The participant began a regime of colchicine (0.6 mg/day) or NSAID prophylaxis at least 1 week before the first dose of pegloticase and continued for the duration of pegloticase therapy. Colchicine prophylaxis was not interrupted during the clinical trial unless medically contraindicated or if the participant became intolerant of colchicine, regardless of whether a gout flare occurs.

Gout Flare Treatment—An increase in gout flares was frequently observed upon initiation of anti-hyperuricemic therapy, including treatment with pegloticase. Participants were instructed to contact the site within 12 hours of the onset of symptoms. Gout flares were confirmed through questioning or direct observation. All participants who experience a gout flare during the study were prescribed anti-inflammatory treatment (e.g., corticosteroids, NSAIDs, colchicine) as deemed clinically indicated by the study physician.

Colchicine may be prescribed in a medically appropriate dose range of 0.6 to 1.8 mg/day, usually dosed as 0.6 mg orally twice per day unless reduced dosing was necessitated by renal insufficiency or gastrointestinal intolerance. The precise dose and regimen of colchicine was individualized for each participant by the investigators, such as in the case of renal insufficiency where colchicine was appropriately started at 0.6 mg/day and increased to three times a day as tolerated.

Example 7

Statistical Methods

The co-primary aims of our initial double-blind, placebo-controlled study were to 1) assess the feasibility of a course of immune modulating therapy with daily methotrexate (MTX). We tested the hypothesis that MTX safely attenuated immunogenicity conferred by pegloticase as determined by the proportion of participants achieving and maintaining an SUA ≤to 6 mg/dL, compared to concurrent controls. The proportion of participants achieving and maintaining an SUA ≤to 5 mg/dL, compared to concurrent controls was also determined. After co-administration, all participants continued on pegloticase for an additional course of KXX without combination MTX therapy to evaluate the longer-term benefits and safety of this approach; and 2) Assess the incidence and types of adverse events/infusion reactions.

Data Management—The DCC has extensive experience in data management in over approximately 15 active national/international collaborative studies. The data management systems and approaches employed for RECIPE were based on existing, highly successful platforms. The MITS Suite (a distributed data management system) consists of the MITS Studio (electronic Data Entry Management System [eDEMS] Authoring Tool) and the Testing Framework. The clinical centers were responsible for the entry and management of data from their own center, providing cost-effective (as it removes practically all of the query process) higher quality data.

Validation of data—Validation of data was done using the MITS Suite, which contains mechanisms to ensure accuracy, reliability, and the ability to discern invalid or altered records.

Data Analysis—Primary Aims

One of the primary objectives of this study was to determine if there was an overall reduction in immunogenicity leading to increased responders (i.e., enhanced response rate) to pegloticase when MTX was co-administered in adults with chronic refractory gout. This primary objective can be assessed by estimation of the response rate during month 6 (weeks 20, 22, and 24), as measured by the sustained normalization of serum uric acid (SUA) to <6 mg/dL for at least 80% of the time during month 6 in subjects receiving pegloticase with MTX. A decision table was prepared indicating when sufficient evidence was present to move forward to a full-scale clinical trial. Comparison may be made comparing the success rates in peg+MTX versus peg+PBO.

Statistical Analysis on Efficacy Parameters

Efficacy analyses were performed using the modified intention-to-treat (mITT) population, defined as all enrolled subjects who received ≥1 dose of pegloticase. The proportion of Month 6 responders was summarized, along with a 95% confidence interval for the proportion. The proportion of Month 3 and overall (Months 3 and 6 combined) responders was analyzed similarly.

A subject was declared a non-responder if the subject had SUA level >6 mg/dL at 2 consecutive study visits beginning with the Week 2 Visit. In addition, a subject who withdraws from study treatment for any reason after the first dose of pegloticase in the KXX+MTX Period and prior to Month 6 (for the primary endpoint) or Month 3 (for the secondary endpoint) was considered a non-responder if SUA values were not collected at the planned time points.

Swollen/tender joint counts, HAQ scores, patient and physician global assessment scores, subject assessment of joint pain scores, and mean SUA changes from baseline and values at baseline and each visit were summarized with descriptive statistics. The proportion of subjects achieving 20%, 50%, or 70% improvement based on gout chronic response criteria were summarized. For subjects with DECT scans, changes from baseline and values at Weeks 24, 36 and 52 for urate volume were summarized with descriptive statistics.

Other statistical methods may be used as necessary to analyze the data. Participants before the primary endpoint that do not tolerate MTX, or were lost to follow-up, withdraw, or were otherwise not evaluable were counted as failures but not non-responders in sensitivity analyses.

In the event of missing antibody data, imputations were considered to assure data completeness for our analyses using PROC MI and PROC MIANALYZE procedures with 5 replicates per value. All analyses were conducted using SAS (V9.4, Cary, N.C.).

Data Analysis—Secondary Aims and Safety Aims.

The secondary and safety aims were to: 1) Determine the 6 month durability of immune modulation after discontinuation of the course of MTX by: a) assessing the absolute change in SUA from baseline to specific timepoints during treatment with KXX and MTX, and b) determining the proportion of participants with SUA ≤6 mg/dL throughout the study; 2) Identify and characterize the pegloticase immune response by immunoglobulin isotypes (IgG and IgM), specificities, and antibody titer, and 3) Examine patient reported outcomes (PROs) using the NIH supported Patient Reported Outcomes Measurement Information System (PROMIS) and Gout Impact Scale (GIS) instruments.

Example 8

Adverse Events (AEs)

This study examines two medications (pegloticase and MTX) that were already FDA approved and have been in clinical use for over 5 years but were not commonly co-administered. An AE was defined as any untoward event, whether or not it was considered related to the use of pegloticase or MTX. Any worsening (i.e., any clinically significant adverse change in frequency or intensity) of a preexisting condition which was temporally associated with the use of pegloticase or MTX was also considered an AE. Abnormal laboratory values or test results constitute AEs only if they induce clinical signs or symptoms or require therapy, and were recorded on the AE CRF under the signs, symptoms or were associated with diagnoses associated with them. Screening conditions were not considered AE; however, worsening of a preexisting condition may be considered an AE. AEs were collected starting at the baseline, Visit 1.

The safety events of interest in assessing study risks and benefits were IRs and a co-primary study outcome. Participants were followed for the occurrence of IR and secondary outcomes of interest events at each study visit. Supplementing the data collected during these visits was information collected regarding participant reported health-related quality of life (QOL), and for improved, near real-time assessment of outcome events. Non-severe/serious events that were expected according to previous experience with the study drugs (pegloticase, MTX) as described in the protocol, consent materials, or any approved product labelling were also collected. All severe/serious AEs were reported according to appropriate authority (e.g., FDA, IRB) in compliance with guidelines and regulations.

Expected AEs Associated with KXX

An AE that was not an unexpected AE was an infusion reaction and rarely anaphylaxis. Safety assessments in this study include an evaluation of the frequency and severity of IRs and anaphylaxis. During pre-marketing controlled clinical trials, infusion reactions were reported in 26% of patients treated with pegloticase 8 mg every 2 weeks. During pre-marketing controlled clinical trials, anaphylaxis was reported with a frequency of 6.5% of patients treated with pegloticase. For the purposes of this study, these events shall be defined as follows:

IR—not attributable to another cause that occurs during or within 2 hours after the infusion of pegloticase was defined as an AE. Other cases that occur outside of the 2-hour window may also be categorized as an IR as per site PI discretion.

Anaphylaxis was defined using the National Institute of Allergy and Infectious Diseases (NIAID)/Food Allergy and Anaphylaxis Network (FAAN) criteria: acute onset of an illness (minutes to several hours) with involvement of the skin, mucosal tissue, or both (e.g., generalized hives; pruritus or flushing; urticarial, and angioedema (of lips, tongue, or uvula) and at least one of the following: Hypotension (i.e., systolic blood pressure <90 mm Hg or >30% decrease from that person's screening) or associated symptoms of end-organ failure (e.g., hypotonia [collapse], syncope, incontinence; persistent gastrointestinal symptoms (e.g., crampy, abdominal pain, vomiting), and respiratory compromise (e.g., dyspnea, bronchospasm, stridor, reduced peak expiratory flow, hypoxemia).

Pegloticase has not been formally studied in patients with congestive heart failure, but some patients in clinical trials have experienced exacerbation. Patients who had diagnosed congestive heart failure were not enrolled in the study. It is common for potent urate lowering therapies to lead to acute attacks of gout. Other uncommon symptoms reported in at least 5% patients treated with pegloticase that may occur during the study period were ecchymoses, sore throat, constipation, chest pain, and vomiting.

Expected AEs Associated with MTX

Gastrointestinal: Nausea and vomiting (RA: 12%), diarrhea;

Hematologic & oncologic: Leukopenia (renal transplant: >50%; RA: 28%), neoplasia (renal transplant 3% (other than lymphoma), 0.5% (lymphoma)), thrombocytopenia;

Hepatic: Hepatotoxicity, increased serum alkaline phosphatase, increased serum bilirubin, increased serum transaminases;

Infection: Increased susceptibility to infection (renal transplant 20%; RA <1%; includes bacterial, fungal, protozoal, viral, opportunistic, and reactivation of latent infections)

Expected AEs Associated with Colchicine

Participants taking colchicine for gout flare prophylaxis may experience gastrointestinal intolerance which may lead to nausea, persistent diarrhea, and/or gastrointestinal bleeding. The most commonly reported side effects for the prophylaxis of gout was diarrhea (23%) and pharyngolaryngeal pain (3%).

Other AEs associated with colchicine include: Neutropenia, leading to an increased risk of infection; Anemia; Myalgia or myositis; Alopecia; Pruritus; Neuropathy; Oligospermia.

While taking colchicine participants should avoid eating grapefruit and Seville oranges or drinking grapefruit juice or Seville orange juice. These can increase their chances of getting serious side effects.

Serious Adverse Event (SAE) Criteria

A SAE is any AE occurring at any dose that results in any of the following outcomes: Death; Is life-threatening (places the participant, in the view of the site PI, at immediate risk of death from the AE as it occurred); Inpatient hospitalization or prolongation of existing hospitalization (hospitalization is defined as an inpatient admission, regardless of length of stay, even if hospitalized as a precautionary measure for continued observation); A permanent, persistent, or significant disability (substantial disruption of the ability to conduct normal life functions). A medically significant AE that may jeopardize the participant and may require medical or surgical intervention to prevent one of the outcomes listed in this definition

Events NOT considered to be Severe or Serious AEs are: Hospitalization for treatment, which was elective or pre-planned, for a pre-existing condition that did not worsen; Treatment on an emergency, outpatient basis for an event NOT fulfilling any of the definitions of serious given above and NOT resulting in hospital admission; An event that, had it occurred in a more severe form, might have caused death; A sign, symptom, or event that is noticeable but easily tolerated; An event does not significantly influence performance or prevent the participant from carrying on with usual life activities.

Infusion Reaction Prophylaxis

Since IRs can occur with pegloticase, all subjects received IR prophylaxis prior to each infusion, consisting of an antihistamine, acetaminophen, and a corticosteroid. To standardize this regimen, subjects received fexofenadine (60 mg or 180 mg orally based on the Principal Investigator's discretion) the day before each infusion; fexofenadine (60 mg or 180 mg orally based on the Principal Investigator's discretion) and acetaminophen (1000 mg orally) the morning of each infusion; and methylprednisolone (125 mg IV) given over the infusion duration 10-30 minutes (recommended) or hydrocortisone (200 mg IV) was administered immediately prior to each infusion.

Infusion Reaction Treatment

Subjects were monitored closely for signs and symptoms of IRs. In the event of an IR, the infusion should be slowed, or stopped, and restarted at a slower rate at the discretion of the Investigator. If a serious IR occurs, the infusion should be discontinued and treatment should be provided as needed.

If a subject experiences an AE suspected to be an IR:

A physical examination was performed to capture medically relevant details, including, but not limited to, a thorough dermatologic examination for detection of erythema, urticaria (hives), or peri-oral or lingual edema; a chest examination for breath sounds, stridor or wheezing; and a cardiac examination with attention to irregular heartbeat.

Vital signs (sitting or supine blood pressure, heart rate, respiratory rate, and body temperature) were captured at least every 30 minutes until the resolution or stabilization of the AE.

A serum sample was collected in a serum-separating tube at that time or at the subsequent visit. The sample was centrifuged, frozen at -20° C. or colder, and stored for the batch shipment to a Horizon designated laboratory for evaluation of pegloticase antibodies at a future date.

If, in the Investigator's opinion, the subject was experiencing an anaphylactic reaction, pegloticase was immediately discontinued. Any incidence of anaphylaxis was reported as an SAE.

The Investigator may administer any medically indicated pharmacologic agent or procedure intended to relieve symptoms.

After the first incidence of an IR that does not meet the criteria of anaphylaxis or does not meet serious criteria, the Investigator may elect to initiate the next infusion at a slower rate. Additionally, the Investigator may choose to prescribe prednisone (e.g., 20 mg) to be taken in the morning of the next infusion. All changes to infusion rate or dilution, and drugs given for prophylaxis or treatment, were to be recorded in the medical record and in the eCRF.

Example 9

Discontinuation and Participant Withdrawal

Due to the risk of anaphylaxis and IRs being higher in patients who have lost therapeutic response, participants with SUA levels above 6 mg/dL at 2 consecutive visits shall be classified as a non-responder and discontinued from the study. Investigators obtained a pre-dose SUA sample for all patients and reviewed results to verify the SUA level was ≤6 mg/dL prior to infusion.

Participants could withdraw their consent and discontinue the study at any time by informing the study coordinator. Following OHRP guidance and recommendations on this topic (hhs.gov/ohrp/policy/subjectwithdrawal.html#), if a subject decided to withdraw, we inquired as to whether the subject wished to withdraw from all components of the trial or only from the primary intervention. If the latter, we encouraged continuation on follow-up data collection activities for which the subject previously gave consent. These data may prove very useful Moreover, we documented each case of withdrawal, whether it was based on the decision of the participant or investigator (e.g., non-compliance), and whether the withdrawal was from all study components or only the primary intervention.

If the study drug was discontinued, unless the subject withdrew consent, the subject was followed for the full study period and all data were collected as scheduled. Participants that were lost to follow-up or withdraw and do not provide data informative to the primary study were replaced. This may include but was not limited to the following reasons: (1) The subject deciding to withdraw consent for study; (2) An intolerable AE as judged by study site PI and participant; (3) The subject discontinuing acceptable birth control methods or becoming pregnant; (4) The subject enrolling in a conflicting investigational drug trial.

In the event a participant was lost to follow-up, withdraws consent and discontinues the study before the end and was therefore unable to contribute to the primary outcome, the enrolling site was afforded the opportunity to enroll a replacement participant. Attempts were made to schedule an early end of study assessment in the case of study drug discontinuation.

As stated above, premenopausal women had a pregnancy test before the study started and again throughout the study. If participants suspected that they may have become pregnant during the study, the study coordinator contacted the study PI immediately and the PI or Study Coordinator instructed the participant to stop taking all study medication. If it was confirmed that the participant was pregnant, they were withdrawn from the study. The study PI scheduled a follow-up visit and followed the outcome of the pregnancy. If it was discovered that participants were breastfeeding, they were not eligible to participate in the study and their participation was discontinued immediately.

Based on the known safety profiles of pegloticase and MTX and the procedures in place, it is very unlikely, but possible, that we could witness one severe AE related to infection. We instituted a stopping rule for safety re-evaluation that would occur if we register more than one of such severe adverse reaction (e.g., infection that leads to hospitalization). We then stopped the study to comprehensively review safety and our study protocols in conjunction with the DSMB. Other severe adverse reaction or deaths may or may not be related to the study and stopping or discontinuation of the study was considered on an individual basis.

Example 10

Randomized, Double-Blind, Placebo-Controlled, Multicenter, Efficacy and Safety Study of MTX to Increase Response Rates in Patients with Uncontrolled Gout Receiving KXX

The overall objective of this study was to assess the potential for pegloticase with MTX to increase the response rate seen with pegloticase alone, and to characterize the safety, tolerability and pharmacokinetics (PK) of the concomitant use of pegloticase with MTX, by comparing pegloticase co-administered with MTX to pegloticase co-administered with placebo for MTX in adults with uncontrolled gout.

Primary Objective: The primary objective was to evaluate the effect of pegloticase with MTX vs. pegloticase with placebo for MTX on the response rate during Month 6 (Weeks 20, 21, 22, 23 and 24), as measured by the sustained normalization of SUA) to <6 mg/dL for at least 80% of the time during Month 6.

Secondary Objectives (Analyzed Sequentially):

Evaluate the effect of pegloticase with MTX vs. pegloticase with placebo for MTX on the response rate during Month 9 (Weeks 32, 34, and 36), as measured by the sustained normalization of SUA to <6 mg/dL for at least 80% of the time during Month 9.

Evaluate the effect of pegloticase with MTX vs. pegloticase with placebo for MTX on the response rate during Month 12 (Weeks 48, 50, and 52), as measured by the sustained normalization of SUA to <6 mg/dL for at least 80% of the time during Month 12.

Evaluate the effect of pegloticase with MTX vs. pegloticase with placebo for MTX on the complete resolution of ≥1 tophi (using digital photography) at Week 52 in subjects with tophi at baseline.

Exploratory Objectives

Evaluate the effect of pegloticase with MTX vs. pegloticase with placebo for MTX on the mean change from baseline in urate deposition volume and bone erosions due to gout to Weeks 14, 24, and 52 based on dual-energy computed tomography (DECT) of the hands and feet.

Evaluate the effect of pegloticase with MTX vs. pegloticase with placebo for MTX on the mean change from baseline in bone erosions due to gout to Weeks 24 and 52 based on X-rays of the hands and feet.

Evaluate the effect of pegloticase with MTX vs. pegloticase with placebo for MTX on the complete resolution of ≥1 tophi (using digital photography) at Weeks 24 and 36 in subjects with tophi at baseline.

Evaluate the effect of pegloticase with MTX vs. pegloticase with placebo for MTX on the mean change from baseline in tophus size (long axis measured using digital photography) to Weeks 14, 24, 36 and 52 in subjects with tophus present at baseline.

Evaluate the effect of pegloticase with MTX vs. pegloticase with placebo for MTX on the response rate during Month 3 (Weeks 10, 12 and 14), as measured by the sustained normalization of SUA to <6 mg/dL for at least 80% of the time during Month 3. Evaluate the effect of pegloticase with MTX vs. pegloticase with placebo for MTX on the overall response rate, as measured by the sustained normalization of SUA to <6 mg/dL for at least 80% of the time during Month 3 (Weeks 10, 12, and 14) and Month 6 (Weeks 20, 21, 22, 23, and 24) combined.

Evaluate the effect of pegloticase with MTX vs. pegloticase with placebo for MTX on reducing SUA to <5 mg/dL for at least 80% of the time during Months 3, 6, 9 and 12, individually.

Evaluate the effect of pegloticase with MTX vs. pegloticase with placebo for MTX on the mean change from baseline in SUA at Weeks 14, 24, 36 and 52.

Evaluate the effect of pegloticase with MTX vs. pegloticase with placebo for MTX on the time to first SUA >6 mg/dL.

Evaluate the effect of pegloticase with MTX vs. pegloticase with placebo for MTX on the time to two consecutive SUA >6 mg/dL (SUA stopping rule).

Evaluate the effect of pegloticase with MTX vs. pegloticase with placebo for MTX on the percentage of non-hyperuricemic (SUA <6 mg/dL) time during Months 3, 6, 9 and 12.

Evaluate the effect of pegloticase with MTX vs. pegloticase with placebo for MTX on the mean change from baseline in HAQ Pain Score at Weeks 14, 24, 36 and 52.

Evaluate the effect of pegloticase with MTX vs. pegloticase with placebo for MTX on the mean change from baseline in HAQ Health Score at Weeks 14, 24, 36 and 52.

Evaluate the effect of pegloticase and MTX vs. pegloticase and placebo for MTX on the mean change from baseline in HAQ-DI Score at Weeks 14, 24, 36 and 52.

Evaluate the effect of pegloticase with MTX vs. pegloticase with placebo for MTX on the mean change from baseline in tender joint count (68-point scale) at Weeks 14, 24, 36 and 52.

Evaluate the effect of pegloticase with MTX vs. pegloticase with placebo for MTX on the mean change from baseline in swollen joint count (66-point scale) at Weeks 14, 24, 36 and 52.

Evaluate the effect of pegloticase with MTX vs. pegloticase with placebo for MTX on the mean change from baseline in number of tender or swollen joints at Weeks 14, 24, 36 and 52.

Evaluate the effect of pegloticase with MTX vs. pegloticase with placebo for MTX on the mean change from baseline in physician global assessment of gout at Weeks 14, 24, 36 and 52.

Evaluate the effect of pegloticase with MTX vs. pegloticase with placebo for MTX on the proportion of subjects achieving 20%, 50%, or 70% improvement based on gout chronic response criteria at Weeks 14, 24, 36 and 52.

Evaluate the effect of pegloticase with MTX vs. pegloticase with placebo for MTX on the proportion of subjects whose treatment goals were met at Weeks 24 and 52.

Evaluate the effect of pegloticase with MTX vs. pegloticase with placebo for MTX on the mean change from baseline in systolic blood pressure (SBP) and diastolic blood pressure (DBP) to each visit.

Assess the PK of pegloticase.

Assess the incidence of anti-PEG and anti-Uricase IgG antibodies.

Safety and Tolerability Objectives

AE/SAE profile overall for pegloticase and the combination of pegloticase and MTX: Incidence of AESI: IRs, anaphylaxis, gout flares, cardiovascular events

Laboratory tests

Vital signs and physical examination

Study Design

This study was a Phase 4, multicenter, randomized, double-blind, placebo-controlled, parallel-group, efficacy and safety study of pegloticase with MTX vs. pegloticase with placebo for MTX in adult subjects with uncontrolled gout.

The study design included: 1) a Screening Period (screening should be completed within 4 weeks prior to Week −6); 2) a 2-week MTX Tolerability Assessment Period consisting of 2 weeks oral MTX for all subjects; 3) a Run-In Period consisting of randomization followed by 4 weeks of blinded oral MTX or placebo for MTX; 4) a 52-week Pegloticase+IMM Period; 5) a Safety Follow-up (Phone/Email/Site Visit) and 6) a 3 and 6 month Post Treatment Follow-up. The Sponsor, Investigator, study site personnel and study subject remained blinded to each subject's treatment assignment (MTX or placebo for MTX)

All subjects who met eligibility criteria at Screening began 15 mg MTX orally weekly at the Week −6 visit. Subjects also took folic acid 1 mg orally every day beginning during the MTX Tolerability Assessment Period (Week −6 to Week −4) and continuing until prior to the Week 52 Visit.

Subjects had to be able to tolerate the weekly dose of MTX 15 mg for 2 weeks to be eligible to be randomized at Week −4. Subjects who were unable to tolerate the 15 mg dose of MTX during the 2 weeks preceding the Week −4 visit were considered screen failures.

Subjects who tolerate the weekly 15 mg MTX dose during the 2 weeks preceding Week −4 Visit and continue to meet eligibility criteria were randomized at the Week −4 Visit in a 2:1 ratio (stratified by presence of tophi) to receive either blinded oral 15 mg MTX or blinded oral placebo for MTX. Subjects continued to take the blinded MTX or placebo for MTX from Week −4 to Day 1 (the Run-in period) at the 15 mg MTX or placebo for MTX dose. If a subject does not tolerate the 15 mg MTX or placebo for MTX dose after randomization at the Week −4 Visit and prior to Day 1, the MTX or placebo for MTX may be dose-reduced or discontinued based on pre-specified criteria and after discussion with the Sponsor medical monitor. The subject was allowed to remain in the study. After Day 1, MTX or placebo for MTX may be re-initiated. The subject was re-initiated to the same treatment they were randomized to at Week −4. The re-initiated MTX or placebo for MTX remained blinded.

All subjects who completed the Run-In Period received the first pegloticase infusion on Day 1. All subsequent doses and study visits were scheduled based on the Day 1 visit date.

It was required that before a subject begins the pegloticase+IMM Period, he or she had been taking at least one protocol standard gout flare prophylaxis regimen (i.e., colchicine and/or non-steroidal anti-inflammatory drugs and/or low-dose prednisone ≤10 mg/day) for ≥1 week before the first dose of pegloticase and continues flare prophylaxis per American College of Rheumatology guidelines [Khanna D et al. 2012] for the greater of 1) 6 months, 2) 3 months after achieving target serum urate (SUA <6 mg/dL) for patients with no tophi detected on physical exam, or 3) 6 months after achieving target serum urate (SUA <5 mg/dL) for patients with one or more tophi detected on initial physical exam that had since resolved. For IR prophylaxis, fexofenadine (180 mg orally) was taken the day before each infusion; fexofenadine (180 mg orally) and acetaminophen (1000 mg orally) were taken the morning of each infusion; and methylprednisolone (125 mg IV) given over an infusion duration between 10-30 minutes, immediately prior to each infusion.

During the Pegloticase+IMM Period, pegloticase 8 mg was administered intravenously (IV) every 2 weeks from Day 1 through the Week 50 Visit for a total of 26 infusions; pegloticase was administered after all pre-dose study visit assessments were completed at each visit. The date and start and stop time of infusion were recorded. Serum uric acid stopping rules were applied: subjects with SUA level >6 mg/dL at 2 consecutive study visits beginning with the Week 2 Visit discontinued treatment, complete the End of Pegloticase Infusion Visit procedures within 2 weeks, and continued the subject visits according to the protocol (without treatment).

During the Pegloticase+IMM Period, subjects were instructed to take MTX or placebo for MTX weekly on the same day each week, within 1 to 3 days prior to each pegloticase infusion and one additional weekly dose after the last infusion for subjects who had not stopped pegloticase due to SUA stopping rules; however, if a subject does not do so, MTX or placebo for MTX were taken ≥60 minutes prior to each pegloticase infusion.

After Day 1, if a subject became unable to tolerate MTX or placebo for MTX, the MTX or placebo for MTX dose was reduced and/or discontinued based on pre-defined criteria, and the subject remained in the study.

The Investigator reviewed the clinical status and individual subject treatment goals at Screening, Week 24, the End of Pegloticase Infusions Visit (if applicable) or the Week 52/End of Study/Early Termination Visit.

After the Week 52 Visit (or End of Pegloticase Infusion Visit [if applicable]), subjects should resume regular care for gout per the judgment of the treating physician, including resumption of ULT upon pegloticase discontinuation, if appropriate. Subjects had a 3- and 6-Month Follow-up visit to assess clinical status, including SUA levels.

Samples for measurement of SUA levels, PK analysis of pegloticase, pegloticase immunogenicity and MTX Polyglutamate analysis were collected at specific visits.

Safety assessments, including monitoring and recording of all AEs, whether drug-related or not, measurement of vital signs, physical examinations, and monitoring of hematology and blood chemistry, were performed. The total blood volume to be collected from each subject during this study was approximately 850 mL.

An external Data Monitoring Committee (DMC) was convened to review data for safety and efficacy with timing and criteria outlined in the DMC Charter, with the possibility of DMC recommendation on study conduct modification per criteria also to be outlined in the Charter.

An independent external adjudication committee reviewed reported events of infusion reactions, cardiovascular events and anaphylaxis.

Subject Population: Subjects eligible for this study had SUA ≥7 mg/dL and gout refractory to conventional therapy characterized by failure to normalize serum uric acid despite conventional therapy or contraindication to conventional therapy, and ongoing symptoms of gout including one of the following: visible tophi, recurrent gout flares, or chronic gouty arthropathy.

Inclusion Criteria:

Eligible subjects must meet/provide all the following criteria:

Willing and able to give informed consent.

Willing and able to comply with the prescribed treatment protocol and evaluations for the duration of the study.

Adult men or women ≥18 years of age.

Uncontrolled gout, defined as meeting the following criteria:

Hyperuricemia during the screening period defined as SUA ≥7 mg/dL, and;

Failure to maintain normalization of SUA with xanthine oxidase inhibitors at the maximum medically appropriate dose, or with a contraindication to xanthine oxidase inhibitor therapy based on medical record review or subject interview, and;

Symptoms of gout including at least 1 of the following:

Presence of at least one tophus

Recurrent flares defined as 2 or more flares in the past 12 months prior to screening

Presence of chronic gouty arthritis

Willing to discontinue any oral urate lowering therapy for at least 7 days prior to MTX dosing at Week −6 and remain off when receiving pegloticase infusions.

Women of childbearing potential (including those with an onset of menopause <2 years prior to screening, non-therapy-induced amenorrhea for <12 months prior to screening, or not surgically sterile [absence of ovaries and/or uterus]) must have negative serum/urine pregnancy tests during Screening and Week −6; subjects must agree to use 2 reliable forms of contraception during the study, one of which was recommended to be hormonal, such as an oral contraceptive. Hormonal contraception were started ≥1 full cycle prior to Week −4 (start of MTX) and continue for 30 days after the last dose of pegloticase, or at least one ovulatory cycle after the last dose of MTX or placebo for MTX (whichever was the longest duration after the last dose of pegloticase or MTX or placebo for MTX). Highly effective contraceptive methods (with a failure rate <1% per year), when used consistently and correctly, include implants, injectables, combined oral contraceptives, some intrauterine devices, sexual abstinence, or vasectomized partner.

Men who were not vasectomized must agree to use appropriate contraception so as to not impregnate a female partner of reproductive potential during the study and for at least 3 months after the last dose of MTX or placebo for MTX.

Able to tolerate MTX 15 mg orally for 2 to 4 weeks during the screening/MTX Run-in period prior to the first dose of KXX.

Exclusion Criteria

Subjects were ineligible for study participation if they meet any of the following criteria:

Weight >160 kg (352 pounds) at Screening.

Any serious acute bacterial infection, unless treated and completely resolved with antibiotics at least 2 weeks prior to the Week −6 Visit.

Severe chronic or recurrent bacterial infections, such as recurrent pneumonia or chronic bronchiectasis.

Current or chronic treatment with systemic immunosuppressive agents such as MTX, azathioprine, or mycophenolate mofetil; prednisone ≥10 mg/day or equivalent dose of other corticosteroid on a chronic basis (3 months or longer) would also meet exclusion criteria.

History of any transplant surgery requiring maintenance immunosuppressive therapy.

Known history of hepatitis B virus surface antigen positivity or hepatitis B DNA positivity.

Known history of hepatitis C virus RNA positivity.

Known history of Human Immunodeficiency Virus (HIV) positivity.

Glucose-6-phosphate dehydrogenase deficiency (tested at the Screening Visit).

Chronic renal impairment defined as estimated glomerular filtration rate (eGFR) <40 mL/min/1.73 m² or currently on dialysis.

Non-compensated congestive heart failure or hospitalization for congestive heart failure within 3 months of the Screening Visit, uncontrolled arrhythmia, treatment for acute coronary syndrome (myocardial infarction or unstable angina), or uncontrolled blood pressure (>160/100 mmHg) prior to Randomization at Week −4.

Pregnant, planning to become pregnant, breastfeeding, planning to impregnate female partner, or not on an effective form of birth control, as determined by the Investigator.

Prior treatment with pegloticase, another recombinant uricase (rasburicase), or concomitant therapy with a polyethylene glycol-conjugated drug.

Known allergy to pegylated products or history of anaphylactic reaction to a recombinant protein or porcine product.

Contraindication to MTX treatment or MTX treatment considered inappropriate.

Known immunogenicity of MTX.

Receipt of an investigational drug within 4 weeks or 5 half-lives, whichever was longer, prior to MTX administration at Week -6 or plans to take an investigational drug during the study.

Liver transaminase levels (AST or ALT) >upper limit of normal (ULN) or albumin <the lower limit of normal (LLN) at the Screening Visit.

Chronic liver disease.

White blood cell count <4,000/ul, hematocrit <32 percent, or platelet count <75,000/ul.

Currently receiving systemic or radiologic treatment for ongoing cancer.

History of malignancy within 5 years other than non-melanoma skin cancer or in situ carcinoma of cervix.

Diagnosis of osteomyelitis.

Known history of hypoxanthine-guanine phosphoribosyl-transferase deficiency, such as Lesch-Nyhan and Kelley-Seegmiller syndrome.

Unsuitable candidate for the study, based on the opinion of the Investigator (e.g., cognitive impairment), such that participation might create undue risk to the subject or interfere with the subject's ability to comply with the protocol requirements or complete the study.

Alcohol use in excess of 3 alcoholic beverages per week.

A known intolerance to at least one protocol standard gout flare prophylaxis regimen (i.e., colchicine and/or non-steroidal anti-inflammatory drugs and/or low-dose prednisone ≤10 mg/day).

Current pulmonary fibrosis, bronchiectasis or interstitial pneumonitis. If deemed necessary by the Investigator, a chest X-ray may be performed during Screening.

Dose Regimen/Route of Administration:

MTX or placebo for MTX:

During the MTX Tolerability Assessment Period (Week −6 until the Week −4 visit), all subjects took MTX 15 mg orally weekly.

At the Week −4 visit, subjects who tolerated MTX were randomized to receive MTX 15 mg or placebo for MTX orally weekly. Subjects were blinded to MTX or placebo for MTX beginning at Week −4 through the remainder of the study. Subjects continued to take the blinded MTX or placebo for MTX during the Run-in Period (from Week −4 to Day 1) at the 15 mg MTX dose or placebo for MTX dose. If a subject did not tolerate the 15 mg MTX or placebo for MTX dose after randomization at the Week −4 Visit and prior to Day 1, the MTX or placebo for MTX may be dose-reduced or discontinued based on pre-specified criteria and after discussion with the Sponsor medical monitor. The subject was allowed to remain in the study. After Day 1, MTX or placebo for MTX may be re-initiated. The subject was re-initiated to the same treatment they were randomized to at Week −4. The re-initiated MTX or placebo for MTX remained blinded. During the Run-in Period, if a dose was missed, it was taken as soon as it was remembered. If it was within 48 hours of the next scheduled dose, the subject was instructed to skip the missed dose and resume at the next regularly scheduled time; thus, subjects were instructed not to double a dose to make up for a missed dose if within 48 hours of the next dose.

During the Pegloticase+IMM Period, subjects were instructed to take MTX or placebo for MTX weekly on the same day each week, within 1 to 3 days prior to each pegloticase infusion and one additional weekly dose after the last infusion for subjects who had not stopped pegloticase due to SUA stopping rules; however, if a subject does not do so, MTX or placebo for MTX were taken ≥60 minutes prior to each pegloticase infusion. If a subject becomes unable to tolerate the MTX or placebo for MTX during the Pegloticase+IMM Period, the dosage may be decreased.

Subjects also took folic acid 1 mg orally every day beginning during the MTX Tolerability assessment (Week −6 to Week −4) and continuing until prior to the Week 52 Visit.

Pegloticase:

All subjects who meet the inclusion/exclusion criteria and complete the Run-In Period received pegloticase at a dose of 8 mg administered IV every 2 weeks for a total of 26 infusions from Day 1 through the Week 50 Visit, inclusive (Pegloticase+IMM Period). The date and start and stop time of infusion were recorded. Subjects were not fasting on the day of infusion and were encouraged to have a snack or normal meal before or after the infusion. All subjects received standardized prophylactic treatment to reduce the risk of acute gout flares, beginning ≥1 week before the first dose of pegloticase and continues flare prophylaxis per American College of Rheumatology guidelines [Khanna D et al. 2012] for the greater of 1) 6 months, 2) 3 months after achieving target serum urate (SUA <6 mg/dL) for patients with no tophi detected on physical exam, or 3) 6 months after achieving target serum urate (SUA <5 mg/dL) for patients with one or more tophi detected on initial physical exam that had since resolved. Standardized IR prophylaxis consisting of pre-treatment with antihistamines, acetaminophen and corticosteroids accompanied each infusion.

Dosage Form and Strength Formulation (Pegloticase, MTX and Placebo for MTX):

Pegloticase (KRYSTEXXA) is commercially available in the United States and was packaged in sterile, single-use 2-mL glass vials with a Teflon®-coated (latex-free) rubber injection stopper to deliver pegloticase as 8 mg of uricase protein in 1 mL volume. Pegloticase was administered as an admixture of 8 mg in 250 mL of 0.45% or 0.9% Sodium Chloride Injection, United States Pharmacopeia (USP) for IV infusion by gravity feed or infusion pump. Pegloticase was not administered as an IV push or bolus.

MTX 2.5 mg tablets for oral administration during the MTX Tolerability Assessment Period (Week −6 through Week −4) were provided to subjects as a commercially available generic.

MTX 2.5 mg tablets for oral administration during the Run-In Period (Week −4 through Day 1) and the Pegloticase+IMM Period (Day 1 through Week 52) were provided to subjects as a methotrexate 2.5 mg tablet over-encapsulated in a size zero Swedish Orange capsule.

Placebo for methotrexate 2.5 mg for oral administration during the Run-In Period (Week −4 through Day 1) and the Pegloticase+IMM Period (Day 1 through Week 52) were provided as a size zero Swedish Orange capsule with Avicel® filling

Duration of Treatment and Follow-up:

Screening: Completed within 4 weeks prior to the Week −6 visit

MTX Tolerability Assessment Period (Week −6 through Week −4): 2 weeks of oral MTX for all subjects

Run-in Period (Week −4 through Day 1): Randomization followed by 4 weeks of blinded oral MTX or placebo for MTX.

Pegloticase+IMM Period (Day 1 through Week 52): MTX or placebo for MTX dosed weekly and 50 weeks of pegloticase infusion visits every 2 weeks; Non-infusion visits at Weeks 21, 23 and 52.

End of Pegloticase Infusions Visit (if applicable): If the subject discontinued pegloticase treatment prior to infusion Week 50, such as due to the SUA stopping rules, the subject completed this visit within approximately 2 weeks of the last infusion. Subjects continued in the study.

End of Study/Early Termination Visit: Week 52 or earlier if the subject withdraws consent to participate in the study.

Safety Follow-up Phone/Email Visit or Visit: All subjects received a safety follow-up phone call/e-mail approximately 30 days after the last dose of pegloticase to assess if any SAE's occurred. Subjects who receive at least one dose of MTX or placebo for MTX and were females of childbearing potential, received a safety follow-up phone call/e-mail approximately 30 days after the last dose of MTX or placebo for MTX to verify at least one ovulatory cycle had occurred after the last dose of MTX or placebo for MTX. If the subject had not ovulated, a urine pregnancy test was performed. Subjects who receive at least one dose of MTX and were non-vasectomized males, a phone/e-mail inquiry were conducted 3 months after MTX discontinuation regarding partner pregnancy (inquiry can occur during the 3-month Post Treatment Follow-up).

3- and 6-Month Post Treatment Follow-up: All subjects were followed for a minimum of 6 months following the last infusion, with follow-up after Week 52 as warranted.

Criteria for Evaluation:

Efficacy was assessed by SUA levels, tophus resolution, tophus size, tender and swollen joint counts, physician global assessment of gout, and DECT and X-ray of hands and feet.

Quality of life was assessed using the HAQ.

The PK of pegloticase was assessed prior to and after the pegloticase infusion at specified time points.

Pegloticase immunogenicity was assessed by the incidence of anti-PEG and anti-uricase IgG antibodies prior to the pegloticase infusion at specified time points.

Safety assessments included monitoring and recording of all AEs, whether drug-related or not, measurement of vital signs, physical examinations, and monitoring of hematology and blood chemistry.

Statistical Analyses:

Primary Efficacy Endpoint

The primary efficacy endpoint was the proportion of Month 6 (Weeks 20, 21, 22, 23 and 24) responders, defined as subjects achieving and maintaining SUA <6 mg/dL for at least 80% of the time during Month 6.

Secondary Efficacy Endpoints

The secondary endpoints were analyzed sequentially:

The proportion of Month 9 (Weeks 32, 34, and 36) responders, defined as subjects achieving and maintaining SUA <6 mg/dL for at least 80% of the time during Month 9.

The proportion of Month 12 (Weeks 48, 50, and 52) responders, defined as subjects achieving and maintaining SUA <6 mg/dL for at least 80% of the time during Month 12.

The proportion of subjects with complete resolution of ≥1 tophi (using digital photography) at Week 52 in subjects with tophi at baseline.

Exploratory Efficacy Endpoints

The mean change from baseline to Weeks 14, 24 and 52 in urate volume and bone erosions due to gout based on DECT of the hands and feet.

The mean change from baseline to Weeks 24 and 52 in bone erosions due to gout based on X-rays of the hands and feet.

The proportion of subjects with complete resolution of ≥1 tophi (using digital photography) at Weeks 24 and 36 in subjects with tophi at baseline.

The mean change from baseline in tophus size (long axis measured using digital photography) to Weeks 14, 24, 36 and 52 in subjects with tophus present at baseline.

The proportion of Month 3 (Weeks 10, 12, and 14) responders, defined as subjects achieving and maintaining SUA <6 mg/dL for at least 80% of the time during Month 3.

The proportion of overall responders, defined as subjects achieving and maintaining SUA <6 mg/dL for at least 80% of the time during Month 3 (Weeks 10, 12, and 14) and Month 6 (Weeks 20, 21, 22, 23 and 24) combined.

The proportion of 5 mg/dL responders during each time interval (Month 3, Month 6, Month 9 and Month 12), defined as subjects achieving and maintaining SUA <5 mg/dL for at least 80% of the time during each time interval.

The mean change from baseline in SUA at Weeks 14, 24, 36 and 52.

The time to first SUA >6 mg/dL.

The time to two consecutive SUA >6 mg/dL (stopping rule).

The percentage of non-hyperuricemic (SUA <6 mg/dL) time during Months 3, 6, 9 and 12.

The mean change from baseline in HAQ Pain score at Weeks 14, 24, 36 and 52.

The mean change from baseline in HAQ Health score at Weeks 14, 24, 36 and 52.

The mean change from baseline in HAQ-DI score at Weeks 14, 24, 36 and 52.

The mean change from baseline in tender joint count (68-point scale) at Weeks 14, 24, 36 and 52.

The mean change from baseline in swollen joint count (66-point scale) at Weeks 14, 24, 36 and 52.

The mean change from baseline in number of tender or swollen joints at Weeks 14, 24, 36 and 52.

The mean change from baseline in physician global assessment of gout at Weeks 14, 24, 36 and 52.

The proportion of subjects achieving 20%, 50%, or 70% improvement based on gout chronic response criteria at Weeks 14, 24, 36 and 52.

The proportion of subjects whose treatment goals were met at Weeks 24 and 52.

The change from baseline in SBP and DBP to each visit.

Pharmacokinetic and Anti-Drug Antibody Endpoints

PK of pegloticase.

The incidence of anti-PEG and anti-Uricase IgG antibodies.

Safety and Tolerability Objectives

AE/SAE profile overall for pegloticase and the combination of pegloticase and MTX: Incidence of AESI: IRs, anaphylaxis, gout flares, cardiovascular events

Laboratory tests

Vital signs and physical examination

Statistical Analysis on Efficacy Parameters

The primary analysis was conducted in the Intent-to-Treat (ITT) population, defined as all randomized subjects. The primary efficacy endpoint was the proportion of responders during Month 6. A responder was defined as a subject for whom the proportion of time that the SUA-time curve was <6 mg/dL during the analysis interval was at least 80%. The proportion of time that the SUA level was below 6 mg/dL was defined as the ratio of the time during which the SUA level remains below 6 mg/dL (using linear interpolation, if necessary) to the entire time interval during Month 6. A subject was declared a non-responder if the subject had an SUA level >6 mg/dL at 2 consecutive study visits beginning with the Week 2 Visit prior to or during Month 6. Additionally, a subject who withdraws from study treatment for any reason after randomization and prior to or during Month 6 (for the primary endpoint) or Months 3, 9 or 12 (for the secondary and exploratory endpoints) was considered a non-responder at the time of withdrawal.

The analysis of the primary responder endpoint assessed risk difference (difference in response proportions) in a stratified analysis. The analysis used Cochran-Mantel-Haenszel (CMH) weighting to estimate the common risk difference within strata and to estimate the standard error of the common risk difference. Stratification for the analysis used the same factor as was used to stratify randomization, presence of tophi (yes, no). The difference in response rates, comparing pegloticase with MTX vs. pegloticase with placebo for MTX, was estimated along with the corresponding 95% confidence interval (CI) and p-value.

The proportion of Month 9 responders and Month 12 responders was analyzed similarly. The difference in the proportion of subjects with resolution of ≥1 tophi (100% decrease in the area of at least 1 tophus) at Week 52 between pegloticase and placebo was tested with a chi-square test, and the difference in rates was estimated along with the corresponding 95% CI and p-value.

HAQ-DI score, HAQ Pain and Health scores, tophus size (longest axis), urate volume (DECT), joint erosions due to gout using DECT (hands and feet), joint erosions due to gout using X-ray (hands and feet), swollen/tender joint counts, physician global assessment score, and SUA were summarized at baseline and each visit with descriptive statistics. Changes from baseline for these parameters to each visit and overall were analyzed with a mixed model repeated measures (MMRM) analysis of covariance (ANCOVA) model with a term for baseline score, and factors for treatment group, visit, and visit by treatment group interaction. Baseline was defined as the last observation prior to the first dose of MTX. The proportion of subjects achieving 20%, 50%, or 70% improvement based on gout chronic response criteria were analyzed with a CMH test.

Interim Analysis

An interim analysis was undertaken when all subjects had reached the Week 24 visit. An independent DMC was convened to oversee and interpret this analysis to assess the primary endpoint of maintaining SUA

<6 mg/dL at least 80% of the time during Month 6 (Weeks 20, 21, 22, 23 and 24) comparing pegloticase with MTX to pegloticase with placebo for MTX, as well as to assess the safety of the co-administration of pegloticase with MTX based on all accrued data at that time. The DMC recommended unblinding the Sponsor, stopping the study, or continuing without change at the time of the interim analysis, based on pre-defined criteria. In the event of a highly clinically compelling increase in response rates with pegloticase with MTX vs pegloticase with placebo for MTX, and in the absence of any unexpected safety findings, the Sponsor may become unblinded for full data analysis. Subjects would continue on study through Week 52, with investigators and subjects remaining blinded. Clear parameters to guide decision criteria were pre-specified in advance. Upon all subjects reaching Week 52, a final analysis was completed in which the secondary endpoints were tested, including maintaining SUA <6 mg/dL at least 80% of the time during Month 9, maintaining SUA <6 mg/dL at least 80% of the time during Month 12, and proportion of subjects with complete resolution of at least one tophus by digital photography through Week 24. Additional safety data accrued would also be summarized.

Criteria would also established and pre-specified for the DMC to recommend study discontinuation due to futility or an unexpected safety risk. An interim analysis for futility may be completed earlier on the basis of the MIRROR Open-Label study results. At the futility analysis there was no opportunity to conclude a benefit of MTX and therefore there was no adjustment to the Type I error.

If none of the above scenarios were established, the study would continue, and the Sponsor would remain blinded until all subjects reach Week 52.

Sample Size Estimate: The response rate during Month 6 on pegloticase 8 mg every 2 weeks was 43% for the phase 3 studies. A sample size of 135 subjects (90 subjects randomized to receive pegloticase with MTX, 45 subjects randomized to receive pegloticase with placebo for MTX) provides 88% power at the 2-sided alpha=0.05 level to detect a difference of 28% (71% response rate for pegloticase with MTX vs. 43% for pegloticase with placebo for MTX).

Removal of Subjects From Therapy or Study: All subjects were free to withdraw from study participation at any time, for any reason, and without prejudice to their further medical care. In addition, the Investigator may terminate a subject from the study at any time. However, subjects who were removed from pegloticase therapy should remain on study barring withdrawal of consent for study participation.

Removal of Subjects From Pegloticase Therapy: In addition to completion of therapy through Week 52, the reason for discontinuation from the therapy should be recorded on the eCRF using 1 of the following categories:

Lack of Efficacy. (i.e., SUA level >6 mg/dL at 2 consecutive study visits beginning with the Week 2 Visit).

Adverse Event. The subject experiences an AE that imposes an unacceptable risk to the subject's health (e.g., anaphylactic reaction), or the subject was unwilling to continue therapy because of an AE. Subjects who discontinue due to an AE should be followed until resolution or stabilization of the AE, or an adequate explanation for the event was obtained.

The Investigator determined that pegloticase administration poses an unacceptable risk to the subject (specify reason).

Subject refusal of additional therapy (specify reason).

Study Terminated by Sponsor. The Sponsor, IRB, or regulatory agency terminates the study.

Pregnancy

Death

Study Considerations for Subjects Ending Pegloticase Infusions Prior to 52 Weeks:

Methotrexate/placebo for MTX, along with folic acid, were discontinued at the time of cessation of pegloticase infusions prior to Week 52.

All subjects completed the End of Pegloticase Infusions Visit and remained on study through Week 52 regardless of whether they stop infusions due to SUA stopping rules or other reason (e.g., withdrawal of consent for pegloticase infusions).

Subjects were encouraged to continue to participate in all visits through the end of the study. Subjects were especially encouraged to complete study visits at the study site during key efficacy and safety collections at Weeks 20, 21, 22, 23, 24, 32, 34, 36, 48, 50 and 52, so that SUA labs and other key assessments can be completed. During visits between these key efficacy and safety collection visits, in subjects who had stopped infusions, subjects may complete study visits in person or via telephone to collect AEs, concomitant medications, and gout flare information.

Activities related to pre/post infusion monitoring or medication dispensation were not completed once a subject stopped pegloticase infusions. These activities include:

MTX/placebo for MTX compliance/reconciliation

Infusion reaction prophylaxis

IR prophylaxis compliance

Folic acid compliance

Pegloticase infusion

Pegloticase PK sampling

Pre-infusion MTX Polyglutamate sampling

MTX drug/dispensation related items Post Treatment Follow-up: The intent was to obtain at least 6 months of follow-up on each subject after cessation of pegloticase infusions. If these 6 months occur prior to end of study at Week 52, such as in the case of a subject who ends pegloticase infusions on or before Week 24, there were no follow-up visits after the Week 52/End of Study Visit. For subjects who end pegloticase infusions between Weeks 26 and 36, there were at least 3 months of follow-up while the subject remains on-study prior to Week 52, and then one follow-up visit after the Week 52/End of Study Visit. For subjects who end pegloticase infusions between Weeks 38 and 52, there were two follow-up visits at intervals of 3 months apart after the Week 52/End of Study Visit.

Gout flare prophylaxis and treatment, and infusion reaction prophylaxis and treatment are described herein elsewhere.

Screen failure criteria are described herein elsewhere.

Serum samples for measurement of SUA levels were collected at the Screening Visit, the Week −6 Visit (prior to the first dose of MTX), the Week −4 Visit (Randomization) and the Week −2 Visit during the Run-in Period; within 48 hours prior to each pegloticase infusion and after the end of each pegloticase infusion prior to discharge from the site during the Pegloticase+IMM Period on Day 1, at the Weeks 2, 6, 10, 12, 14, 20, 22, 24, 32, 34, 36, 48 and 50; within 48 hours prior to each pegloticase infusion at Weeks 4, 8, 16, 18, 26, 28, 30, 38, 40, 42, 44 and 46. Additional serum samples for SUA levels were collected at non-infusion Visits at Weeks 21 and 23 and the End of Pegloticase Infusions Visit (if applicable) and the Week 52/End of study/Early Termination Visit and 3 and 6 month Follow-up Visits. Subjects with an SUA level >6 mg/dL at 2 consecutive study visits beginning with the Week 2 Visit discontinued pegloticase and completed the End of Pegloticase Infusions Visit (if applicable) or the Week 52/End of study/Early Termination Visit procedures.

Study Procedures

Screening/MTX Tolerability Assessment/Run-in Period

During the Screening/MTX Tolerability Assessment Period, study candidates were evaluated for study entry according to the stated inclusion and exclusion criteria. The following procedures were performed during screening to establish each candidate's eligibility for enrollment into the study.

Screening Visit (Within 2 Weeks Prior to the First Dose of MTX at Week -6)

Obtain signed, written informed consent. Refusal to provide this permission excludes an individual from eligibility for study participation. Record date informed consent was given and who conducted the process on the appropriate source documentation.

Determine study eligibility through review of the inclusion/exclusion criteria.

Obtain demographic information

Investigator review of clinical status and subject treatment goals.

Collect complete gout history (on gout-specific CRF), other relevant medical/surgical history, and medication history, including gout medications starting at the time of diagnosis and up to screening (on gout medications-specific CRF), substance use history, and all other medications currently being taken at screening.

Chest X-ray for subjects that did not have a chest X-ray within 2 years prior to Screening if deemed necessary by the Investigator.

Perform a complete physical examination, including assessment of HEENT, heart, lungs, abdomen, skin, extremities, neurological status and musculoskeletal including an assessment for the presence of tophi.

Document gout flares and intensity.

Record vital signs (blood pressure, respiratory rate, temperature, and heart rate

Record height and weight.

Perform 12-lead ECG.

Obtain blood samples for hematology and clinical chemistry analysis.

Obtain a serum sample from all females of childbearing potential for performance of a pregnancy test.

Obtain blood samples to evaluate SUA (only 1 sample for central laboratory) and G6PD.

Administer HAQ and record physician global assessments.

Inquire about AEs and concomitant medication use.

Week −6 (MTX Tolerability Assessment Period)

Confirm study eligibility through review of the inclusion/exclusion criteria.

Perform a targeted physical examination (at a minimum this should include heart, lungs and abdominal examination).

Record vital signs (blood pressure, respiratory rate, temperature, and heart rate).

Record weight.

Document gout flares and intensity.

Collect swollen/tender joint counts; administer HAQ; and record physician global assessments.

Digital photography of hands and feet.

Obtain blood samples for hematology and clinical chemistry analysis.

Obtain a urine sample from all females of childbearing potential for performance of a pregnancy test.

Obtain a blood sample for measurement of SUA (only 1 sample for central laboratory).

Obtain optional whole blood and serum samples from subjects who consent for future analysis.

Provide dosing calendar for subjects to record the date and time they take MTX/placebo for MTX. (Additional calendar pages may be provided at future visits as needed).

Dispense MTX.

Fill gout prophylaxis, fexofenadine, acetaminophen, and folic acid prescriptions, as needed.

Inquire about AEs and concomitant medication use.

Subjects that take MTX during Week −6 or Week −5, and who were females of childbearing potential, received a safety follow-up phone call/e-mail approximately 30 days after the last dose of MTX to verify at least one ovulatory cycle occurred since the last dose of MTX. If the subject had not ovulated, a urine pregnancy test was performed. Subjects who were non-vasectomized males, an inquiry was conducted approximately 3 months after MTX discontinuation regarding partner pregnancy.

Week −4 (Run-in Period)

Confirm study eligibility through review of the inclusion/exclusion criteria.

Document gout flares and intensity.

Record vital signs (blood pressure, respiratory rate, temperature, and heart rate).

Obtain blood samples for hematology and clinical chemistry analysis.

Obtain a urine sample from all females of childbearing potential for performance of a pregnancy test.

Obtain a blood sample for measurement of SUA (only 1 sample for central laboratory).

Assess MTX compliance (from MTX Tolerability Assessment Period)

Dispense MTX/placebo for MTX.

Ask Yes/No question regarding folic acid and gout flare prophylaxis compliance.

Fill gout prophylaxis, fexofenadine, acetaminophen, and folic acid prescriptions, as needed.

Inquire about AEs and concomitant medication use.

Randomization in RTMS to MTX or placebo for MTX.

Subjects that take MTX/placebo for MTX during Week −4 or Week −3, and who were females of childbearing potential, received a safety follow-up phone call/e-mail approximately 30 days after the last dose of MTX/placebo for MTX to verify at least one ovulatory cycle had occurred since the last dose of MTX/placebo for MTX. If the subject had not ovulated, a urine pregnancy test was performed. Subjects who were non-vasectomized males, an inquiry was conducted approximately 3 months after MTX/placebo for MTX discontinuation regarding partner pregnancy. Week −2 (Run-in Period)

Obtain a urine sample from all females of childbearing potential for performance of a pregnancy test.

Obtain a blood sample for measurement of SUA (only 1 sample for central laboratory).

Obtain blood samples for hematology and clinical chemistry analysis.

Assess MTX/placebo for MTX compliance and re-dispense MTX/placebo for MTX.

Ask Yes/No question regarding folic acid and gout flare prophylaxis compliance.

Fill gout prophylaxis, fexofenadine, acetaminophen, and folic acid prescriptions, as needed.

Inquire about AEs and concomitant medication use.

Subjects that take MTX/placebo for MTX during Week -2 or Week -1, and who were females of childbearing potential, received a safety follow-up phone call/e-mail approximately 30 days after the last dose of MTX/placebo for MTX to verify at least one ovulatory cycle occurred since the last dose of MTX/placebo for MTX. If the subject had not ovulated, a urine pregnancy test was performed. Subjects who were non-vasectomized males, an inquiry was conducted approximately 3 months after MTX/placebo for MTX discontinuation regarding partner pregnancy.

Pegloticase+IMM Period

Day 1

On Day 1, subjects returned to the clinic for the following assessments and the first dose of pegloticase.

Perform a targeted physical examination (at a minimum this should include heart, lungs and abdominal examination).

Record vital signs (blood pressure, respiratory rate, temperature, and heart rate) prior to the pegloticase infusion and any time after the end of the infusion, but prior to discharge. During the pre-infusion blood pressure collection, at sites who participate and from subjects who consent, optional intensive BP collections were obtained. For this optional collection, three blood pressure measurements should be performed, at least 2 minutes apart, with BP readings measured to the nearest mm Hg prior to pegloticase infusion. If any of the 3 systolic blood pressure measurements differed by more than 8 mm Hg or if diastolic measurements differed by more than 5 mm Hg, a second set of 3 sitting blood pressure measurements was obtained.

Record weight.

Digital photography of hands and feet.

For sites with X-ray capability, and subjects who provide consent, an optional X-ray of the hands and feet was obtained.

Document gout flares and intensity.

Collect swollen/tender joint counts; administer HAQ; and record physician global assessments.

For sites with DECT capability, and subjects who provide consent, an optional DECT was obtained. DECT may be completed within +/−5 days of the scheduled visit.

Obtain blood samples for hematology and clinical chemistry analysis.

Obtain a urine sample for albumin:creatinine ratio and allantoin acid.

Obtain a urine sample from all females of childbearing potential for performance of a pregnancy test.

Obtain 1 blood sample for measurement of SUA prior to the pegloticase infusion and after the end of the pegloticase infusion.

Assess MTX/placebo for MTX compliance and re-dispense MTX/placebo for MTX.

Ask Yes/No question regarding folic acid, gout flare prophylaxis, and IR prophylaxis compliance.

Fill gout prophylaxis, fexofenadine, acetaminophen, and folic acid prescriptions, as needed.

Administer MTX/placebo for MTX ≥60 minutes prior to pegloticase infusion if subject had not taken MTX/placebo for MTX within the previous 1 to 3 days.

Obtain blood samples for MTX Polyglutamate analysis prior to the infusion.

Obtain blood samples for anti-PEG and anti-uricase IgG antibodies prior to the infusion.

Obtain optional whole blood and serum samples from subjects who consent for future analysis.

Administer IR prophylaxis (i.e., fexofenadine, acetaminophen, and solumedrol).

Administer the first dose of pegloticase and record date, volume, and duration of infusion, and start/stop (inclusive of 10-mL flush) times of dosing.

Obtain blood samples for pegloticase PK analysis any time after the end of the infusion, prior to discharge from the site.

Inquire about AEs and concomitant medication use.

Week 2

Obtain 2 blood samples for measurement of SUA within 48 hours prior to this visit's pegloticase infusion. Pre-infusion SUA results were reported by the local or central laboratory prior to pegloticase infusion. If a local laboratory sample was drawn at a center other than the research site (within 48 hours prior to the pegloticase infusion), a sample for the central laboratory was drawn prior to the pegloticase infusion on the day of the visit.

Administer MTX/placebo for MTX ≥60 minutes prior to pegloticase infusion if subject had not taken MTX within the previous 1 to 3 days.

Document gout flares and intensity.

Record vital signs (blood pressure, respiratory rate, temperature, and heart rate) prior to the pegloticase infusion and any time after the end of the infusion, but prior to discharge.

Assess MTX/placebo for MTX compliance and re-dispense MTX/placebo for MTX.

Ask Yes/No question regarding folic acid, gout flare prophylaxis, and IR prophylaxis compliance.

Fill gout prophylaxis, fexofenadine, acetaminophen, and folic acid prescriptions, as needed.

Obtain blood samples for hematology and clinical chemistry analysis.

Obtain a urine sample from all females of childbearing potential for performance of a pregnancy test.

Obtain blood samples for pegloticase PK analysis prior to the pegloticase infusion and any time after the end of the infusion, prior to discharge from the site.

Obtain blood samples for anti-PEG and anti-uricase IgG antibodies prior to the infusion.

Obtain optional whole blood and serum samples from subjects who consent for future analysis. Samples were only collected at this visit for subjects having an acute gout flare during this visit.

Administer IR prophylaxis (i.e., fexofenadine, acetaminophen, and methylprednisolone).

Administer pegloticase and record date, volume, and duration of infusion, and start/stop (inclusive of 10-mL flush) times of dosing.

Obtain a blood sample (1 sample) for measurement of SUA any time after the end of the infusion, prior to discharge from the site.

Inquire about AEs and concomitant medication use.

Week 4

Obtain 2 blood samples for measurement of SUA within 48 hours prior to this visit's pegloticase infusion. Pre-infusion SUA results were reported by the local or central laboratory prior to pegloticase infusion. If a local laboratory sample was drawn at a center other than the research site (within 48 hours prior to the pegloticase infusion), a sample for the central laboratory was drawn prior to the pegloticase infusion on the day of the visit.

Stopping rule: Subjects with an SUA level >6 mg/dL at 2 consecutive study visits beginning with the Week 2 Visit (not including post-infusion samples) subsequently discontinued treatment and remained in the study.

Administer MTX/placebo for MTX ≥60 minutes prior to pegloticase infusion if subject had not taken MTX/placebo for MTX within the previous 1 to 3 days.

Perform a targeted physical examination (at a minimum this should include heart, lungs and abdominal examination).

Document gout flares and intensity.

Record vital signs (blood pressure, respiratory rate, temperature, and heart rate) prior to the pegloticase infusion and any time after the end of the infusion, but prior to discharge.

Assess MTX/placebo for MTX compliance and re-dispense MTX/placebo for MTX.

Ask Yes/No question regarding folic acid, gout flare prophylaxis, and IR prophylaxis compliance.

Fill gout prophylaxis, fexofenadine, acetaminophen, and folic acid prescriptions, as needed.

Obtain a urine sample from all females of childbearing potential for performance of a pregnancy test.

Obtain optional whole blood and serum samples from subjects who consent for future analysis. Samples were only collected at this visit for subjects having an acute gout flare during this visit.

Administer IR prophylaxis (i.e., fexofenadine, acetaminophen, and methylprednisolone).

Administer pegloticase and record date, volume, and duration of infusion, and start/stop (inclusive of 10-mL flush) times of dosing.

Inquire about AEs and concomitant medication use.

Week 6

Obtain 2 blood samples for measurement of SUA within 48 hours prior to this visit's pegloticase infusion. Pre-infusion SUA results were reported by the local or central laboratory prior to pegloticase infusion. If a local laboratory sample was drawn at a center other than the research site (within 48 hours prior to the pegloticase infusion), a sample for the central laboratory was drawn prior to the pegloticase infusion on the day of the visit.

Stopping rule: Subjects with an SUA level >6 mg/dL at 2 consecutive study visits beginning with the Week 2 Visit (not including post-infusion samples) subsequently discontinued treatment and remained in the study.

Administer MTX/placebo for MTX ≥60 minutes prior to pegloticase infusion if subject had not taken MTX/placebo for MTX within the previous 1 to 3 days.

Document gout flares and intensity.

Record vital signs (blood pressure, respiratory rate, temperature, and heart rate) prior to the pegloticase infusion and any time after the end of the infusion, but prior to discharge. During the pre-infusion blood pressure collection, at sites who participate and from subjects who consent, optional intensive BP collections were obtained. For this optional collection, three blood pressure measurements should be performed, at least 2 minutes apart, with BP readings measured to the nearest mm Hg prior to pegloticase infusion. If any of the 3 systolic blood pressure measurements differed by more than 8 mm Hg or if diastolic measurements differed by more than 5 mm Hg, a second set of 3 sitting blood pressure measurements was obtained.

Assess MTX/placebo for MTX compliance and re-dispense MTX/placebo for MTX.

Ask Yes/No question regarding folic acid, gout flare prophylaxis, and IR prophylaxis compliance.

Fill gout prophylaxis, fexofenadine, acetaminophen, and folic acid prescriptions, as needed.

Collect swollen/tender joint counts; administer HAQ; and record physician global assessments.

Obtain a urine sample from all females of childbearing potential for performance of a pregnancy test.

Obtain blood samples for hematology and clinical chemistry analysis.

Obtain optional whole blood and serum samples from subjects who consent for future analysis.

Obtain blood samples for pegloticase PK analysis prior to the pegloticase infusion and any time after the end of the infusion, prior to discharge from the site.

Obtain blood samples for anti-PEG and anti-uricase IgG antibodies prior to the infusion.

Administer IR prophylaxis (i.e., fexofenadine, acetaminophen, and methylprednisolone).

Administer pegloticase and record date, volume, and duration of infusion, and start/stop (inclusive of 10-mL flush) times of dosing.

Obtain a blood sample (1 sample) for measurement of SUA any time after the end of the infusion, prior to discharge from the site.

Inquire about AEs and concomitant medication use.

Week 8

Obtain 2 blood samples for measurement of SUA within 48 hours prior to this visit's pegloticase infusion. Pre-infusion SUA results were reported by the local or central laboratory prior to pegloticase infusion. If a local laboratory sample was drawn at a center other than the research site (within 48 hours prior to the pegloticase infusion), a sample for the central laboratory was drawn prior to the pegloticase infusion on the day of the visit.

Stopping rule: Subjects with an SUA level >6 mg/dL at 2 consecutive study visits beginning with the Week 2 Visit (not including post-infusion samples) subsequently discontinued treatment and remained in the study.

Administer MTX/placebo for MTX ≥60 minutes prior to pegloticase infusion if subject had not taken MTX/placebo for MTX within the previous 1 to 3 days.

Perform a targeted physical examination (at a minimum this should include heart, lungs and abdominal examination).

Document gout flares and intensity.

Record weight.

Assess MTX/placebo for MTX compliance and re-dispense MTX/placebo for MTX.

Ask Yes/No question regarding folic acid, gout flare prophylaxis, and IR prophylaxis compliance.

Fill gout prophylaxis, fexofenadine, acetaminophen, and folic acid prescriptions, as needed.

Obtain a urine sample from all females of childbearing potential for performance of a pregnancy test.

Obtain optional whole blood and serum samples from subjects who consent for future analysis. Samples were only collected at this visit for subjects having an acute gout flare during this visit.

Administer IR prophylaxis (i.e., fexofenadine, acetaminophen, and methylprednisolone).

Administer pegloticase and record date, volume, and duration of infusion, and start/stop (inclusive of 10-mL flush) times of dosing.

Inquire about AEs and concomitant medication use.

Week 10

Obtain 2 blood samples for measurement of SUA within 48 hours prior to this visit's pegloticase infusion. Pre-infusion SUA results were reported by the local or central laboratory prior to pegloticase infusion. If a local laboratory sample was drawn at a center other than the research site (within 48 hours prior to the pegloticase infusion), a sample for the central laboratory was drawn prior to the pegloticase infusion on the day of the visit.

Stopping rule: Subjects with an SUA level >6 mg/dL at 2 consecutive study visits beginning with the Week 2 Visit (not including post-infusion samples) subsequently discontinued treatment and remained in the study.

Administer MTX/placebo for MTX ≥60 minutes prior to pegloticase infusion if subject had not taken MTX/placebo for MTX within the previous 1 to 3 days.

Document gout flares and intensity.

Assess MTX/placebo for MTX compliance and re-dispense MTX/placebo for MTX.

Ask Yes/No question regarding folic acid, gout flare prophylaxis, and IR prophylaxis compliance.

Fill gout prophylaxis, fexofenadine, acetaminophen, and folic acid prescriptions, as needed.

Obtain a urine sample from all females of childbearing potential for performance of a pregnancy test.

Obtain optional whole blood and serum samples from subjects who consent for future analysis. Samples were only collected at this visit for subjects having a gout flare during this visit.

Administer IR prophylaxis (i.e., fexofenadine, acetaminophen, and methylprednisolone).

Administer pegloticase and record date, volume, and duration of infusion, and start/stop (inclusive of 10-mL flush) times of dosing.

Obtain a blood sample (1 sample) for measurement of SUA any time after the end of the infusion, prior to discharge from the site.

Inquire about AEs and concomitant medication use.

Week 12

Obtain 2 blood samples for measurement of SUA within 48 hours prior to this visit's pegloticase infusion. Pre-infusion SUA results were reported by the local or central laboratory prior to pegloticase infusion. If a local laboratory sample was drawn at a center other than the research site (within 48 hours prior to the pegloticase infusion), a sample for the central laboratory was drawn prior to the pegloticase infusion on the day of the visit.

Stopping rule: Subjects with an SUA level >6 mg/dL at 2 consecutive study visits beginning with the Week 2 Visit (not including post-infusion samples) subsequently discontinued treatment and remained in the study.

Administer MTX/placebo for MTX ≥60 minutes prior to pegloticase infusion if subject had not taken MTX/placebo for MTX within the previous 1 to 3 days.

Perform a targeted physical examination (at a minimum this should include heart, lungs and abdominal examination).

Document gout flares and intensity.

Record vital signs (blood pressure, respiratory rate, temperature, and heart rate) prior to the pegloticase infusion and any time after the end of the infusion, but prior to discharge. During the pre-infusion blood pressure collection, at sites who participate and from subjects who consent, optional intensive BP collections were obtained. For this optional collection, three blood pressure measurements should be performed, at least 2 minutes apart, with BP readings measured to the nearest mm Hg prior to pegloticase infusion. If any of the 3 systolic blood pressure measurements differed by more than 8 mm Hg or if diastolic measurements differed by more than 5 mm Hg, a second set of 3 sitting blood pressure measurements was obtained.

Assess MTX/placebo for MTX compliance and re-dispense MTX/placebo for MTX.

Ask Yes/No question regarding folic acid, gout flare prophylaxis, and IR prophylaxis compliance.

Fill gout prophylaxis, fexofenadine, acetaminophen, and folic acid prescriptions, as needed.

Obtain a urine sample from all females of childbearing potential for performance of a pregnancy test.

Obtain optional whole blood and serum samples from subjects who consent for future analysis. Samples were only collected at this visit for subjects having an acute gout flare during this visit.

Administer IR prophylaxis (i.e., fexofenadine, acetaminophen, and methylprednisolone).

Administer pegloticase and record date, volume, and duration of infusion, and start/stop (inclusive of 10-mL flush) times of dosing.

Obtain a blood sample (1 sample) for measurement of SUA any time after the end of the infusion, prior to discharge from the site.

Inquire about AEs and concomitant medication use.

Week 14

Obtain 2 blood samples for measurement of SUA within 48 hours prior to this visit's pegloticase infusion. Pre-infusion SUA results were reported by the local or central laboratory prior to pegloticase infusion. If a local laboratory sample was drawn at a center other than the research site (within 48 hours prior to the pegloticase infusion), a sample for the central laboratory was drawn prior to the pegloticase infusion on the day of the visit.

Stopping rule: Subjects with an SUA level >6 mg/dL at 2 consecutive study visits beginning with the Week 2 Visit (not including post-infusion samples) subsequently discontinued treatment and remained in the study.

Administer MTX/placebo for MTX ≥60 minutes prior to pegloticase infusion if subject had not taken MTX/placebo for MTX within the previous 1 to 3 days.

Document gout flares and intensity.

Record vital signs (blood pressure, respiratory rate, temperature, and heart rate) prior to the pegloticase infusion and any time after the end of the infusion, but prior to discharge.

Collect swollen/tender joint counts; administer HAQ; and record physician global assessments.

Digital photography of hands and feet.

For sites with DECT capability, and subjects who provide consent, an optional DECT was obtained. DECT may be completed within +/−5 days of the scheduled visit.

Assess MTX/placebo for MTX compliance and re-dispense MTX/placebo for MTX.

Ask Yes/No question regarding folic acid, gout flare prophylaxis, and IR prophylaxis compliance.

Fill gout prophylaxis, fexofenadine, acetaminophen, and folic acid prescriptions, as needed.

Obtain a urine sample from all females of childbearing potential for performance of a pregnancy test.

Obtain blood samples for hematology and clinical chemistry analysis.

Obtain a urine sample for albumin:creatinine ratio and allantoin acid.

Obtain blood samples for pegloticase PK analysis prior to the pegloticase infusion and any time after the end of the infusion, prior to discharge from the site.

Obtain blood samples for anti-PEG and anti-uricase IgG antibodies prior to the infusion.

Obtain blood samples for MTX Polyglutamate analysis prior to the infusion.

Obtain optional whole blood and serum samples from subjects who consent for future analysis.

Administer IR prophylaxis (i.e., fexofenadine, acetaminophen, and methylprednisolone).

Administer pegloticase and record date, volume, and duration of infusion, and start/stop (inclusive of 10-mL flush) times of dosing.

Obtain a blood sample (1 sample) for measurement of SUA any time after the end of the infusion, prior to discharge from the site.

Inquire about AEs and concomitant medication use.

Week 16

Obtain 2 blood samples for measurement of SUA within 48 hours prior to this visit's pegloticase infusion. Pre-infusion SUA results were reported by the local or central laboratory prior to pegloticase infusion. If a local laboratory sample was drawn at a center other than the research site (within 48 hours prior to the pegloticase infusion), a sample for the central laboratory was drawn prior to the pegloticase infusion on the day of the visit.

Stopping rule: Subjects with an SUA level >6 mg/dL at 2 consecutive study visits beginning with the Week 2 Visit (not including post-infusion samples) subsequently discontinued treatment and remained in the study.

Administer MTX/placebo for MTX ≥60 minutes prior to pegloticase infusion if subject had not taken MTX/placebo for MTX within the previous 1 to 3 days.

Perform a targeted physical examination (at a minimum this should include heart, lungs and abdominal examination).

Document gout flares and intensity.

Record vital signs (blood pressure, respiratory rate, temperature, and heart rate) prior to the pegloticase infusion and any time after the end of the infusion, but prior to discharge.

Record weight.

Assess MTX/placebo for MTX compliance and re-dispense MTX/placebo for MTX.

Ask Yes/No question regarding folic acid, gout flare prophylaxis, and IR prophylaxis compliance.

Fill gout prophylaxis, fexofenadine, acetaminophen, and folic acid prescriptions, as needed.

Obtain a urine sample from all females of childbearing potential for performance of a pregnancy test.

Administer IR prophylaxis (i.e., fexofenadine, acetaminophen, and methylprednisolone).

Administer pegloticase and record date, volume, and duration of infusion, and start/stop (inclusive of 10-mL flush) times of dosing.

Inquire about AEs and concomitant medication use.

Week 18

Obtain 2 blood samples for measurement of SUA within 48 hours prior to this visit's pegloticase infusion. Pre-infusion SUA results were reported by the local or central laboratory prior to pegloticase infusion. If a local laboratory sample was drawn at a center other than the research site (within 48 hours prior to the pegloticase infusion), a sample for the central laboratory was drawn prior to the pegloticase infusion on the day of the visit.

Stopping rule: Subjects with an SUA level >6 mg/dL at 2 consecutive study visits beginning with the Week 2 Visit (not including post-infusion samples) subsequently discontinued treatment and remained in the study.

Administer MTX/placebo for MTX ≥60 minutes prior to pegloticase infusion if subject had not taken MTX/placebo for MTX within the previous 1 to 3 days.

Document gout flares and intensity.

Record vital signs (blood pressure, respiratory rate, temperature, and heart rate) prior to the pegloticase infusion and any time after the end of the infusion, but prior to discharge. During the pre-infusion blood pressure collection, at sites who participate and from subjects who consent, optional intensive BP collections were obtained. For this optional collection, three blood pressure measurements should be performed, at least 2 minutes apart, with BP readings measured to the nearest mm Hg prior to pegloticase infusion. If any of the 3 systolic blood pressure measurements differed by more than 8 mm Hg or if diastolic measurements differed by more than 5 mm Hg, a second set of 3 sitting blood pressure measurements was obtained.

Assess MTX/placebo for MTX compliance and re-dispense MTX/placebo for MTX.

Ask Yes/No question regarding folic acid, gout flare prophylaxis, and IR prophylaxis compliance.

Fill gout prophylaxis, fexofenadine, acetaminophen, and folic acid prescriptions, as needed.

Obtain a urine sample from all females of childbearing potential for performance of a pregnancy test.

Administer IR prophylaxis (i.e., fexofenadine, acetaminophen, and methylprednisolone).

Administer pegloticase and record date, volume, and duration of infusion, and start/stop (inclusive of 10-mL flush) times of dosing.

Inquire about AEs and concomitant medication use.

Week 20

Obtain 2 blood samples for measurement of SUA within 48 hours prior to this visit's pegloticase infusion. Pre-infusion SUA results were reported by the local or central laboratory prior to pegloticase infusion. If a local laboratory sample was drawn at a center other than the research site (within 48 hours prior to the pegloticase infusion), a sample for the central laboratory was drawn prior to the pegloticase infusion on the day of the visit.

Stopping rule: Subjects with an SUA level >6 mg/dL at 2 consecutive study visits beginning with the Week 2 Visit (not including post-infusion samples) subsequently discontinued treatment and remained in the study.

Administer MTX/placebo for MTX ≥60 minutes prior to pegloticase infusion if subject had not taken MTX/placebo for MTX within the previous 1 to 3 days.

Perform a targeted physical examination (at a minimum this should include heart, lungs and abdominal examination).

Document gout flares and intensity.

Record vital signs (blood pressure, respiratory rate, temperature, and heart rate) prior to the pegloticase infusion and any time after the end of the infusion, but prior to discharge.

Assess MTX/placebo for MTX compliance and re-dispense MTX/placebo for MTX.

Ask Yes/No question regarding folic acid, gout flare prophylaxis, and IR prophylaxis compliance.

Fill gout prophylaxis, fexofenadine, acetaminophen, and folic acid prescriptions, as needed.

Collect swollen/tender joint counts; administer HAQ; and record physician global assessments.

Obtain a urine sample from all females of childbearing potential for performance of a pregnancy test.

Administer IR prophylaxis (i.e., fexofenadine, acetaminophen, and methylprednisolone)

Administer pegloticase and record date, volume, and duration of infusion, and start/stop (inclusive of 10-mL flush) times of dosing.

Obtain a blood sample (1 sample) for measurement of SUA any time after the end of the infusion, prior to discharge from the site.

Inquire about AEs and concomitant medication use.

Week 21

Obtain a blood sample (1 sample) for measurement of SUA.

Obtain blood samples for pegloticase PK analysis.

Inquire about AEs and concomitant medication use.

Document gout flares and intensity.

Fill gout prophylaxis, fexofenadine, acetaminophen, and folic acid prescriptions, as needed.

Week 22

Obtain 2 blood samples for measurement of SUA within 48 hours prior to this visit's pegloticase infusion. Pre-infusion SUA results were reported by the local or central laboratory prior to pegloticase infusion. If a local laboratory sample was drawn at a center other than the research site (within 48 hours prior to the pegloticase infusion), a sample for the central laboratory was drawn prior to the pegloticase infusion on the day of the visit.

Stopping rule: Subjects with an SUA level >6 mg/dL at 2 consecutive study visits beginning with the Week 2 Visit (not including post-infusion samples) subsequently discontinued treatment and remained in the study.

Administer MTX/placebo for MTX ≥60 minutes prior to pegloticase infusion if subject had not taken MTX/placebo for MTX within the previous 1 to 3 days.

Document gout flares and intensity.

Record vital signs (blood pressure, respiratory rate, temperature, and heart rate) prior to the pegloticase infusion and any time after the end of the infusion, but prior to discharge.

Assess MTX/placebo for MTX compliance and re-dispense MTX/placebo for MTX.

Ask Yes/No question regarding folic acid, gout flare prophylaxis, and IR prophylaxis compliance.

Fill gout prophylaxis, fexofenadine, acetaminophen, and folic acid prescriptions, as needed.

Obtain a urine sample from all females of childbearing potential for performance of a pregnancy test.

Obtain blood samples for hematology and clinical chemistry analysis.

Obtain blood samples for anti-PEG and anti-uricase IgG antibodies prior to the infusion.

Administer IR prophylaxis (i.e., fexofenadine, acetaminophen, and methylprednisolone).

Administer pegloticase and record date, volume, and duration of infusion, and start/stop (inclusive of 10-mL flush) times of dosing.

Obtain a blood sample (1 sample) for measurement of SUA any time after the end of the infusion, prior to discharge from the site.

Inquire about AEs and concomitant medication use.

Week 23

Obtain a blood sample (1 sample) for measurement of SUA

Inquire about AEs and concomitant medication use.

Document gout flares and intensity.

Fill gout prophylaxis, fexofenadine, acetaminophen, and folic acid prescriptions, as needed.

Week 24

Obtain 2 blood samples for measurement of SUA within 48 hours prior to this visit's pegloticase infusion. Pre-infusion SUA results were reported by the local or central laboratory prior to pegloticase infusion. If a local laboratory sample was drawn at a center other than the research site (within 48 hours prior to the pegloticase infusion), a sample for the central laboratory was drawn prior to the pegloticase infusion on the day of the visit.

Stopping rule: Subjects with an SUA level >6 mg/dL at 2 consecutive study visits beginning with the Week 2 Visit (not including post-infusion samples) subsequently discontinued treatment and remained in the study.

Administer MTX/placebo for MTX ≥60 minutes prior to pegloticase infusion if subject had not taken MTX/placebo for MTX within the previous 1 to 3 days.

Document gout flares and intensity.

Investigator review of clinical status and subject treatment goals.

Perform a targeted physical examination (at a minimum this should include heart, lungs and abdominal examination).

Record vital signs (blood pressure, respiratory rate, temperature, and heart rate) prior to the pegloticase infusion and any time after the end of the infusion, but prior to discharge. During the pre-infusion blood pressure collection, at sites who participate and from subjects who consent, optional intensive BP collections were obtained. For this optional collection, three blood pressure measurements should be performed, at least 2 minutes apart, with BP readings measured to the nearest mm Hg prior to pegloticase infusion. If any of the 3 systolic blood pressure measurements differed by more than 8 mm Hg or if diastolic measurements differed by more than 5 mm Hg, a second set of 3 sitting blood pressure measurements was obtained.

Record weight.

Collect swollen/tender joint counts; administer HAQ; and record physician global assessments.

Digital photography of hands and feet.

For sites with DECT capability, and subjects who provide consent, an optional DECT was obtained. DECT may be completed within +/−5 days of the scheduled visit.

For sites with X-ray capability, and subjects who provide consent, an optional X-ray of the hands and feet was obtained.

Assess MTX/placebo for MTX compliance and re-dispense MTX/placebo for MTX.

Ask Yes/No question regarding folic acid, gout flare prophylaxis, and IR prophylaxis compliance.

Fill gout prophylaxis, fexofenadine, acetaminophen, and folic acid prescriptions, as needed.

Obtain a urine sample from all females of childbearing potential for performance of a pregnancy test.

Obtain blood samples for hematology and clinical chemistry analysis.

Obtain a urine sample for albumin:creatinine ratio and allantoin acid.

Obtain blood samples for pegloticase PK analysis prior to the pegloticase infusion and any time after the end of the infusion, prior to discharge from the site.

Obtain blood samples for anti-PEG and anti-uricase IgG antibodies prior to the infusion.

Obtain blood samples for MTX Polyglutamate analysis prior to the infusion.

Obtain optional whole blood and serum samples from subjects who consent for future analysis.

Administer IR prophylaxis (i.e., fexofenadine, acetaminophen, and methylprednisolone)

Administer pegloticase and record date, volume, and duration of infusion, and start/stop (inclusive of 10-mL flush) times of dosing.

Obtain a blood sample (1 sample) for measurement of SUA any time after the end of the infusion, prior to discharge from the site.

Inquire about AEs and concomitant medication use.

Week 26

Obtain 2 blood samples for measurement of SUA within 48 hours prior to this visit's pegloticase infusion. Pre-infusion SUA results were reported by the local or central laboratory prior to pegloticase infusion. If a local laboratory sample was drawn at a center other than the research site (within 48 hours prior to the pegloticase infusion), a sample for the central laboratory was drawn prior to the pegloticase infusion on the day of the visit.

Stopping rule: Subjects with an SUA level >6 mg/dL at 2 consecutive study visits beginning with the Week 2 Visit (not including post-infusion samples) subsequently discontinued treatment and remained in the study.

Administer MTX/placebo for MTX ≥60 minutes prior to pegloticase infusion if subject had not taken MTX/placebo for MTX within the previous 1 to 3 days.

Document gout flares and intensity.

Record vital signs (blood pressure, respiratory rate, temperature, and heart rate) prior to the pegloticase infusion and any time after the end of the infusion, but prior to discharge.

Assess MTX/placebo for MTX compliance and re-dispense MTX/placebo for MTX.

Ask Yes/No question regarding folic acid, gout flare prophylaxis, and IR prophylaxis compliance.

Fill gout prophylaxis, fexofenadine, acetaminophen, and folic acid prescriptions, as needed.

Obtain a urine sample from all females of childbearing potential for performance of a pregnancy test.

Administer IR prophylaxis (i.e., fexofenadine, acetaminophen, and methylprednisolone)

Administer pegloticase and record date, volume, and duration of infusion, and start/stop (inclusive of 10-mL flush) times of dosing.

Inquire about AEs and concomitant medication use.

Week 28

Obtain 2 blood samples for measurement of SUA within 48 hours prior to this visit's pegloticase infusion. Pre-infusion SUA results were reported by the local or central laboratory prior to pegloticase infusion. If a local laboratory sample was drawn at a center other than the research site (within 48 hours prior to the pegloticase infusion), a sample for the central laboratory was drawn prior to the pegloticase infusion on the day of the visit

Stopping rule: Subjects with an SUA level >6 mg/dL at 2 consecutive study visits beginning with the Week 2 Visit (not including post-infusion samples) subsequently discontinued treatment and remained in the study.

Administer MTX/placebo for MTX ≥60 minutes prior to pegloticase infusion if subject had not taken MTX/placebo for MTX within the previous 1 to 3 days.

Document gout flares and intensity.

Record vital signs (blood pressure, respiratory rate, temperature, and heart rate) prior to the pegloticase infusion and any time after the end of the infusion, but prior to discharge.

Assess MTX/placebo for MTX compliance and re-dispense MTX/placebo for MTX.

Ask Yes/No question regarding folic acid, gout flare prophylaxis, and IR prophylaxis compliance.

Fill gout prophylaxis, fexofenadine, acetaminophen, and folic acid prescriptions, as needed.

Obtain a urine sample from all females of childbearing potential for performance of a pregnancy test.

Administer IR prophylaxis (i.e., fexofenadine, acetaminophen, and methylprednisolone)

Administer pegloticase and record date, volume, and duration of infusion, and start/stop (inclusive of 10-mL flush) times of dosing.

Inquire about AEs and concomitant medication use.

Week 30

Obtain 2 blood samples for measurement of SUA within 48 hours prior to this visit's pegloticase infusion. Pre-infusion SUA results were reported by the local or central laboratory prior to pegloticase infusion. If a local laboratory sample was drawn at a center other than the research site (within 48 hours prior to the pegloticase infusion), a sample for the central laboratory was drawn prior to the pegloticase infusion on the day of the visit.

Stopping rule: Subjects with an SUA level >6 mg/dL at 2 consecutive study visits beginning with the Week 2 Visit (not including post-infusion samples) subsequently discontinued treatment and remained in the study.

Administer MTX/placebo for MTX ≥60 minutes prior to pegloticase infusion if subject had not taken MTX/placebo for MTX within the previous 1 to 3 days.

Document gout flares and intensity.

Record vital signs (blood pressure, respiratory rate, temperature, and heart rate) prior to the pegloticase infusion and any time after the end of the infusion, but prior to discharge. During the pre-infusion blood pressure collection, at sites who participate and from subjects who consent, optional intensive BP collections were obtained. For this optional collection, three blood pressure measurements should be performed, at least 2 minutes apart, with BP readings measured to the nearest mm Hg prior to pegloticase infusion. If any of the 3 systolic blood pressure measurements differed by more than 8 mm Hg or if diastolic measurements differed by more than 5 mm Hg, a second set of 3 sitting blood pressure measurements was obtained.

Assess MTX/placebo for MTX compliance and re-dispense MTX/placebo for MTX.

Ask Yes/No question regarding folic acid, gout flare prophylaxis, and IR prophylaxis compliance.

Fill gout prophylaxis, fexofenadine, acetaminophen, and folic acid prescriptions, as needed.

Collect swollen/tender joint counts; administer HAQ; and record physician global assessments.

Obtain a urine sample from all females of childbearing potential for performance of a pregnancy test.

Administer IR prophylaxis (i.e., fexofenadine, acetaminophen, and methylprednisolone)

Administer pegloticase and record date, volume, and duration of infusion, and start/stop (inclusive of 10-mL flush) times of dosing.

Inquire about AEs and concomitant medication use.

Week 32

Obtain 2 blood samples for measurement of SUA within 48 hours prior to this visit's pegloticase infusion. Pre-infusion SUA results were reported by the local or central laboratory prior to pegloticase infusion. If a local laboratory sample was drawn at a center other than the research site (within 48 hours prior to the pegloticase infusion), a sample for the central laboratory was drawn prior to the pegloticase infusion on the day of the visit.

Stopping rule: Subjects with an SUA level >6 mg/dL at 2 consecutive study visits beginning with the Week 2 Visit (not including post-infusion samples) subsequently discontinued treatment and remained in the study.

Administer MTX/placebo for MTX ≥60 minutes prior to pegloticase infusion if subject had not taken MTX/placebo for MTX within the previous 1 to 3 days.

Document gout flares and intensity.

Record vital signs (blood pressure, respiratory rate, temperature, and heart rate) prior to the pegloticase infusion and any time after the end of the infusion, but prior to discharge.

Assess MTX/placebo for MTX compliance and re-dispense MTX/placebo for MTX.

Ask Yes/No question regarding folic acid, gout flare prophylaxis, and IR prophylaxis compliance.

Fill gout prophylaxis, fexofenadine, acetaminophen, and folic acid prescriptions, as needed.

Obtain a urine sample from all females of childbearing potential for performance of a pregnancy test.

Administer IR prophylaxis (i.e., fexofenadine, acetaminophen, and methylprednisolone).

Administer pegloticase and record date, volume, and duration of infusion, and start/stop (inclusive of 10-mL flush) times of dosing.

Obtain a blood sample (1 sample) for measurement of SUA any time after the end of the infusion, prior to discharge from the site.

Inquire about AEs and concomitant medication use.

Week 34

Obtain 2 blood samples for measurement of SUA within 48 hours prior to this visit's pegloticase infusion. Pre-infusion SUA results were reported by the local or central laboratory prior to pegloticase infusion. If a local laboratory sample was drawn at a center other than the research site (within 48 hours prior to the pegloticase infusion), a sample for the central laboratory was drawn prior to the pegloticase infusion on the day of the visit.

Stopping rule: Subjects with an SUA level >6 mg/dL at 2 consecutive study visits beginning with the Week 2 Visit (not including post-infusion samples) subsequently discontinued treatment and remained in the study.

Administer MTX/placebo for MTX ≥60 minutes prior to pegloticase infusion if subject had not taken MTX/placebo for MTX within the previous 1 to 3 days.

Document gout flares and intensity.

Record vital signs (blood pressure, respiratory rate, temperature, and heart rate) prior to the pegloticase infusion and any time after the end of the infusion, but prior to discharge.

Assess MTX/placebo for MTX compliance and re-dispense MTX/placebo for MTX.

Ask Yes/No question regarding folic acid, gout flare prophylaxis, and IR prophylaxis compliance.

Fill gout prophylaxis, fexofenadine, acetaminophen, and folic acid prescriptions, as needed.

Obtain a urine sample from all females of childbearing potential for performance of a pregnancy test.

Administer IR prophylaxis (i.e., fexofenadine, acetaminophen, and methylprednisolone).

Administer pegloticase and record date, volume, and duration of infusion, and start/stop (inclusive of 10-mL flush) times of dosing.

Obtain a blood sample (1 sample) for measurement of SUA any time after the end of the infusion, prior to discharge from the site.

Inquire about AEs and concomitant medication use.

Week 36

Obtain 2 blood samples for measurement of SUA within 48 hours prior to this visit's pegloticase infusion. Pre-infusion SUA results were reported by the local or central laboratory prior to pegloticase infusion. If a local laboratory sample was drawn at a center other than the research site (within 48 hours prior to the pegloticase infusion), a sample for the central laboratory was drawn prior to the pegloticase infusion on the day of the visit.

Stopping rule: Subjects with an SUA level >6 mg/dL at 2 consecutive study visits beginning with the Week 2 Visit (not including post-infusion samples) subsequently discontinued treatment and remained in the study.

Administer MTX/placebo for MTX ≥60 minutes prior to pegloticase infusion if subject had not taken MTX/placebo for MTX within the previous 1 to 3 days.

Document gout flares and intensity.

Perform a targeted physical examination (at a minimum this should include heart, lungs and abdominal examination).

Record vital signs (blood pressure, respiratory rate, temperature, and heart rate) prior to the pegloticase infusion and any time after the end of the infusion, but prior to discharge. During the pre-infusion blood pressure collection, at sites who participate and from subjects who consent, optional intensive BP collections were obtained. For this optional collection, three blood pressure measurements should be performed, at least 2 minutes apart, with BP readings measured to the nearest mm Hg prior to pegloticase infusion. If any of the 3 systolic blood pressure measurements differed by more than 8 mm Hg or if diastolic measurements differed by more than 5 mm Hg, a second set of 3 sitting blood pressure measurements was obtained.

Record weight.

Collect swollen/tender joint counts; administer HAQ; and record physician global assessments.

Digital photography of hands and feet.

Assess MTX/placebo for MTX compliance and re-dispense MTX/placebo for MTX.

Ask Yes/No question regarding folic acid, gout flare prophylaxis, and IR prophylaxis compliance.

Fill gout prophylaxis, fexofenadine, acetaminophen, and folic acid prescriptions, as needed.

Obtain a urine sample from all females of childbearing potential for performance of a pregnancy test.

Obtain blood samples for hematology and clinical chemistry analysis.

Obtain a urine sample for albumin:creatinine ratio and allantoin acid.

Obtain blood samples for pegloticase PK analysis prior to the pegloticase infusion and any time after the end of the infusion, prior to discharge from the site.

Obtain blood samples for anti-PEG and anti-uricase IgG antibodies prior to the infusion.

Obtain blood samples for MTX Polyglutamate analysis prior to the infusion.

Obtain optional whole blood and serum samples from subjects who consent for future analysis.

Administer IR prophylaxis (i.e., fexofenadine, acetaminophen, and methylprednisolone).

Administer pegloticase and record date, volume, and duration of infusion, and start/stop (inclusive of 10-mL flush) times of dosing.

Obtain a blood sample (1 sample) for measurement of SUA any time after the end of the infusion, prior to discharge from the site.

Inquire about AEs and concomitant medication use.

Week 38

Obtain 2 blood samples for measurement of SUA within 48 hours prior to this visit's pegloticase infusion. Pre-infusion SUA results were reported by the local or central laboratory prior to pegloticase infusion. If a local laboratory sample was drawn at a center other than the research site (within 48 hours prior to the pegloticase infusion), a sample for the central laboratory was drawn prior to the pegloticase infusion on the day of the visit.

Stopping rule: Subjects with an SUA level >6 mg/dL at 2 consecutive study visits beginning with the Week 2 Visit (not including post-infusion samples) subsequently discontinued treatment and remained in the study.

Administer MTX/placebo for MTX ≥60 minutes prior to pegloticase infusion if subject had not taken MTX/placebo for MTX within the previous 1 to 3 days.

Document gout flares and intensity.

Record vital signs (blood pressure, respiratory rate, temperature, and heart rate) prior to the pegloticase infusion and any time after the end of the infusion, but prior to discharge.

Assess MTX/placebo for MTX compliance and re-dispense MTX/placebo for MTX.

Ask Yes/No question regarding folic acid, gout flare prophylaxis, and IR prophylaxis compliance.

Fill gout prophylaxis, fexofenadine, acetaminophen, and folic acid prescriptions, as needed.

Obtain a urine sample from all females of childbearing potential for performance of a pregnancy test.

Administer IR prophylaxis (i.e., fexofenadine, acetaminophen, and methylprednisolone).

Administer pegloticase and record date, volume, and duration of infusion, and start/stop (inclusive of 10-mL flush) times of dosing.

Inquire about AEs and concomitant medication use.

Week 40

Obtain 2 blood samples for measurement of SUA within 48 hours prior to this visit's pegloticase infusion. Pre-infusion SUA results were reported by the local or central laboratory prior to pegloticase infusion. If a local laboratory sample was drawn at a center other than the research site (within 48 hours prior to the pegloticase infusion), a sample for the central laboratory was drawn prior to the pegloticase infusion on the day of the visit.

Stopping rule: Subjects with an SUA level >6 mg/dL at 2 consecutive study visits beginning with the Week 2 Visit (not including post-infusion samples) subsequently discontinued treatment and remained in the study.

Administer MTX/placebo for MTX ≥60 minutes prior to pegloticase infusion if subject had not taken MTX/placebo for MTX within the previous 1 to 3 days.

Document gout flares and intensity.

Record vital signs (blood pressure, respiratory rate, temperature, and heart rate) prior to the pegloticase infusion and any time after the end of the infusion, but prior to discharge.

Assess MTX/placebo for MTX compliance and re-dispense MTX/placebo for MTX.

Ask Yes/No question regarding folic acid, gout flare prophylaxis, and IR prophylaxis compliance.

Fill gout prophylaxis, fexofenadine, acetaminophen, and folic acid prescriptions, as needed.

Obtain a urine sample from all females of childbearing potential for performance of a pregnancy test.

Administer IR prophylaxis (i.e., fexofenadine, acetaminophen, and methylprednisolone).

Administer pegloticase and record date, volume, and duration of infusion, and start/stop (inclusive of 10-mL flush) times of dosing.

Inquire about AEs and concomitant medication use.

Week 42

Obtain 2 blood samples for measurement of SUA within 48 hours prior to this visit's pegloticase infusion. Pre-infusion SUA results were reported by the local or central laboratory prior to pegloticase infusion. If a local laboratory sample was drawn at a center other than the research site (within 48 hours prior to the pegloticase infusion), a sample for the central laboratory was drawn prior to the pegloticase infusion on the day of the visit.

Stopping rule: Subjects with an SUA level >6 mg/dL at 2 consecutive study visits beginning with the Week 2 Visit (not including post-infusion samples) subsequently discontinued treatment and remained in the study.

Administer MTX/placebo for MTX ≥60 minutes prior to pegloticase infusion if subject had not taken MTX/placebo for MTX within the previous 1 to 3 days.

Document gout flares and intensity.

Record vital signs (blood pressure, respiratory rate, temperature, and heart rate) prior to the pegloticase infusion and any time after the end of the infusion, but prior to discharge. During the pre-infusion blood pressure collection, at sites who participate and from subjects who consent, optional intensive BP collections were obtained. For this optional collection, three blood pressure measurements should be performed, at least 2 minutes apart, with BP readings measured to the nearest mm Hg prior to pegloticase infusion. If any of the 3 systolic blood pressure measurements differed by more than 8 mm Hg or if diastolic measurements differed by more than 5 mm Hg, a second set of 3 sitting blood pressure measurements was obtained.

Assess MTX/placebo for MTX compliance and re-dispense MTX/placebo for MTX.

Ask Yes/No question regarding folic acid, gout flare prophylaxis, and IR prophylaxis compliance.

Fill gout prophylaxis, fexofenadine, acetaminophen, and folic acid prescriptions, as needed.

Obtain a urine sample from all females of childbearing potential for performance of a pregnancy test.

Administer IR prophylaxis (i.e., fexofenadine, acetaminophen, and methylprednisolone).

Administer pegloticase and record date, volume, and duration of infusion, and start/stop (inclusive of 10-mL flush) times of dosing.

Inquire about AEs and concomitant medication use.

Week 44

Obtain 2 blood samples for measurement of SUA within 48 hours prior to this visit's pegloticase infusion. Pre-infusion SUA results were reported by the local or central laboratory prior to pegloticase infusion. If a local laboratory sample was drawn at a center other than the research site (within 48 hours prior to the pegloticase infusion), a sample for the central laboratory was drawn prior to the pegloticase infusion on the day of the visit.

Stopping rule: Subjects with an SUA level >6 mg/dL at 2 consecutive study visits beginning with the Week 2 Visit (not including post-infusion samples) subsequently discontinued treatment and remained in the study.

Administer MTX/placebo for MTX ≥60 minutes prior to pegloticase infusion if subject had not taken MTX/placebo for MTX within the previous 1 to 3 days.

Document gout flares and intensity.

Record vital signs (blood pressure, respiratory rate, temperature, and heart rate) prior to the pegloticase infusion and any time after the end of the infusion, but prior to discharge.

Assess MTX/placebo for MTX compliance and re-dispense MTX/placebo for MTX.

Ask Yes/No question regarding folic acid, gout flare prophylaxis, and IR prophylaxis compliance.

Fill gout prophylaxis, fexofenadine, acetaminophen, and folic acid prescriptions, as needed.

Collect swollen/tender joint counts; administer HAQ; and record physician global assessments.

Obtain a urine sample from all females of childbearing potential for performance of a pregnancy test.

Administer IR prophylaxis (i.e., fexofenadine, acetaminophen, and methylprednisolone).

Administer pegloticase and record date, volume, and duration of infusion, and start/stop (inclusive of 10-mL flush) times of dosing.

Inquire about AEs and concomitant medication use.

Week 46

Obtain 2 blood samples for measurement of SUA within 48 hours prior to this visit's pegloticase infusion. Pre-infusion SUA results were reported by the local or central laboratory prior to pegloticase infusion. If a local laboratory sample was drawn at a center other than the research site (within 48 hours prior to the pegloticase infusion), a sample for the central laboratory was drawn prior to the pegloticase infusion on the day of the visit.

Stopping rule: Subjects with an SUA level >6 mg/dL at 2 consecutive study visits beginning with the Week 2 Visit (not including post-infusion samples) subsequently discontinued treatment and remained in the study.

Administer MTX/placebo for MTX ≥60 minutes prior to pegloticase infusion if subject had not taken MTX/placebo for MTX within the previous 1 to 3 days.

Document gout flares and intensity.

Record vital signs (blood pressure, respiratory rate, temperature, and heart rate) prior to the pegloticase infusion and any time after the end of the infusion, but prior to discharge.

Assess MTX/placebo for MTX compliance and re-dispense MTX/placebo for MTX.

Ask Yes/No question regarding folic acid, gout flare prophylaxis, and IR prophylaxis compliance.

Fill gout prophylaxis, fexofenadine, acetaminophen, and folic acid prescriptions, as needed.

Obtain a urine sample from all females of childbearing potential for performance of a pregnancy test.

Administer IR prophylaxis (i.e., fexofenadine, acetaminophen, and methylprednisolone).

Administer pegloticase and record date, volume, and duration of infusion, and start/stop (inclusive of 10-mL flush) times of dosing.

Inquire about AEs and concomitant medication use.

Week 48

Obtain 2 blood samples for measurement of SUA within 48 hours prior to this visit's pegloticase infusion. Pre-infusion SUA results were reported by the local or central laboratory prior to pegloticase infusion. If a local laboratory sample was drawn at a center other than the research site (within 48 hours prior to the pegloticase infusion), a sample for the central laboratory was drawn prior to the pegloticase infusion on the day of the visit.

Stopping rule: Subjects with an SUA level >6 mg/dL at 2 consecutive study visits beginning with the Week 2 Visit (not including post-infusion samples) subsequently discontinued treatment and remained in the study.

Administer MTX/placebo for MTX ≥60 minutes prior to pegloticase infusion if subject had not taken MTX/placebo for MTX within the previous 1 to 3 days.

Document gout flares and intensity.

Record vital signs (blood pressure, respiratory rate, temperature, and heart rate) prior to the pegloticase infusion and any time after the end of the infusion, but prior to discharge. During the pre-infusion blood pressure collection, at sites who participate and from subjects who consent, optional intensive BP collections were obtained. For this optional collection, three blood pressure measurements should be performed, at least 2 minutes apart, with BP readings measured to the nearest mm Hg prior to pegloticase infusion. If any of the 3 systolic blood pressure measurements differed by more than 8 mm Hg or if diastolic measurements differed by more than 5 mm Hg, a second set of 3 sitting blood pressure measurements was obtained.

Assess MTX/placebo for MTX compliance and re-dispense MTX/placebo for MTX.

Ask Yes/No question regarding folic acid, gout flare prophylaxis, and IR prophylaxis compliance.

Fill gout prophylaxis, fexofenadine, acetaminophen, and folic acid prescriptions, as needed.

Obtain a urine sample from all females of childbearing potential for performance of a pregnancy test.

Administer IR prophylaxis (i.e., fexofenadine, acetaminophen, and methylprednisolone).

Administer pegloticase and record date, volume, and duration of infusion, and start/stop (inclusive of 10-mL flush) times of dosing.

Obtain a blood sample (1 sample) for measurement of SUA any time after the end of the infusion, prior to discharge from the site.

Inquire about AEs and concomitant medication use.

Week 50

Obtain 2 blood samples for measurement of SUA within 48 hours prior to this visit's pegloticase infusion. Pre-infusion SUA results were reported by the local or central laboratory prior to pegloticase infusion. If a local laboratory sample was drawn at a center other than the research site (within 48 hours prior to the pegloticase infusion), a sample for the central laboratory was drawn prior to the pegloticase infusion on the day of the visit.

Stopping rule: Subjects with an SUA level >6 mg/dL at 2 consecutive study visits beginning with the Week 2 Visit (not including post-infusion samples) subsequently discontinued treatment and remained in the study.

Administer MTX/placebo for MTX ≥60 minutes prior to pegloticase infusion if subject had not taken MTX/placebo for MTX within the previous 1 to 3 days.

Document gout flares and intensity.

Record vital signs (blood pressure, respiratory rate, temperature, and heart rate) prior to the pegloticase infusion and any time after the end of the infusion, but prior to discharge.

Assess MTX/placebo for MTX compliance and re-dispense MTX/placebo for MTX.

Ask Yes/No question regarding folic acid, gout flare prophylaxis, and IR prophylaxis compliance.

Fill gout prophylaxis, fexofenadine, acetaminophen, and folic acid prescriptions, as needed.

Obtain a urine sample from all females of childbearing potential for performance of a pregnancy test.

Administer IR prophylaxis (i.e., fexofenadine, acetaminophen, and methylprednisolone)

Administer pegloticase and record date, volume, and duration of infusion, and start/stop (inclusive of 10-mL flush) times of dosing.

Obtain a blood sample (1 sample) for measurement of SUA any time after the end of the infusion, prior to discharge from the site.

Inquire about AEs and concomitant medication use.

Note: MTX was taken one week following the Week 50 Visit and Folic Acid was taken until just prior to the Week 52 Visit.

End of Pegloticase Infusions Visit

Subjects who end pegloticase infusions prior to Week 52 completed the End of Pegloticase Infusions Visit procedures following their final infusion. Subjects continued to participate in all visits through the end of the study. Subjects completed selected study visits at the study site during key efficacy and safety collections at Weeks 12, 13, 14, 20, 21, 22, 23, 24, 32, 34, 36, 48, 50 and 52, so that SUA labs and other key assessments could be completed. During visits between these key efficacy and safety collection visits, in subjects who had stopped infusions, subjects could complete study visits in person or via a telephone visit option to collect AEs, concomitant medications, and gout flare information.

The following procedures were completed at the End of Pegloticase Visit:

Investigator review of clinical status and subject treatment goals.

Document gout flares and intensity.

Perform a targeted physical examination (at a minimum this should include heart, lungs and abdominal examination).

Record vital signs (blood pressure, respiratory rate, temperature, and heart rate) prior to the pegloticase infusion and any time after the end of the infusion, but prior to discharge. At sites that participate and from subjects who consent, during the BP collection, optional intensive BP collections were obtained. For this optional collection, three blood pressure measurements should be performed, at least 2 minutes apart, with BP readings measured to the nearest mm Hg prior to pegloticase infusion. If any of the 3 systolic blood pressure measurements differed by more than 8 mm Hg or if diastolic measurements differed by more than 5 mm Hg, a second set of 3 sitting blood pressure measurements was obtained.

Record weight.

Collect swollen/tender joint counts; administer HAQ; and record physician global assessments.

Assess MTX/placebo for MTX compliance.

Ask Yes/No question regarding folic acid, gout flare prophylaxis compliance.

Digital photography of hands and feet.

For sites with DECT capability, and subjects who provide consent, an optional DECT was obtained. DECT may be completed within +/−5 days of the scheduled visit. Subjects who end pegloticase infusions prior to Week 52 should follow the scheduled timepoints but avoid a repeat DECT scan within 6 weeks of a prior scan.

For sites with X-ray capability, and subjects who provide consent, an optional X-ray of the hands and feet was obtained. Subjects who end pegloticase infusions prior to Week 52 should follow the scheduled timepoints but avoid a repeat X-ray within 3 months of a prior X-ray.

Obtain a urine sample from all females of childbearing potential for performance of a pregnancy test.

Obtain blood samples for hematology and clinical chemistry analysis.

Obtain a urine sample for albumin:creatinine ratio and allantoin acid.

Obtain blood samples for pegloticase PK analysis.

Obtain blood samples for anti-PEG and anti-uricase IgG antibodies.

Obtain optional whole blood and serum samples from subjects who consent for future analysis.

Obtain a blood sample (1 sample) for measurement of SUA.

Inquire about AEs and concomitant medication use.

Week 52/End of Study/Early Termination Visit

Investigator review of clinical status and subject treatment goals.

Document gout flares and intensity.

Perform a targeted physical examination (at a minimum this should include heart, lungs and abdominal examination).

Record vital signs (blood pressure, respiratory rate, temperature, and heart rate) prior to the pegloticase infusion and any time after the end of the infusion, but prior to discharge. At sites that participate and from subjects who consent, during the BP collection, optional intensive BP collections were obtained. For this optional collection, three blood pressure measurements should be performed, at least 2 minutes apart, with BP readings measured to the nearest mm Hg prior to pegloticase infusion. If any of the 3 systolic blood pressure measurements differed by more than 8 mm Hg or if diastolic measurements differed by more than 5 mm Hg, a second set of 3 sitting blood pressure measurements was obtained.

Record weight.

Collect swollen/tender joint counts; administer HAQ; and record physician global assessments.

Digital photography of hands and feet.

For sites with DECT capability, and subjects who provide consent, an optional DECT was obtained. DECT may be completed within +/−5 days of the scheduled visit.

For sites with X-ray capability, and subjects who provide consent, an optional X-ray of the hands and feet was obtained.

Assess MTX/placebo for MTX compliance.

Ask Yes/No question regarding folic acid compliance.

Obtain a urine sample from all females of childbearing potential for performance of a pregnancy test.

Obtain blood samples for hematology and clinical chemistry analysis.

Obtain a urine sample for albumin:creatinine ratio and allantoin acid.

Obtain blood samples for pegloticase PK analysis.

Obtain blood samples for anti-PEG and anti-uricase IgG antibodies.

Obtain optional whole blood and serum samples from subjects who consent for future analysis.

Obtain a blood sample (1 sample) for measurement of SUA.

Inquire about AEs and concomitant medication use.

Safety Follow-up Phone/Email Visits

Thirty (30) days after the last pegloticase infusion, subjects were contacted by telephone or email to inquire about SAEs. Subjects who were females of childbearing potential were asked to confirm that ovulation had occurred. If the subject had not ovulated, the subject were requested to return to the site for a urine pregnancy test.

MTX Partner Pregnancy Follow-up

Subjects who were non-vasectomized males were asked 3 months after MTX or placebo for MTX discontinuation regarding partner pregnancy. This occured at a scheduled visit or by a phone/email visit.

Post Treatment Follow-Up

The intent was to obtain at least 6 months of follow-up on each subject after cessation of pegloticase infusions. If these 6 months occur prior to end of study at Week 52, such as in the case of a subject who ends pegloticase infusions on or before Week 24, there were no follow-up visits after the Week 52/End of Study Visit. For subjects who end pegloticase infusions between Weeks 26 and 36, there were at least 3 months of follow-up while the subject remains on-study prior to Week 52, and then one follow-up visit after the Week 52/End of Study Visit.

For subjects who end pegloticase infusions between Weeks 38 and 52, there were two follow-up visits at intervals of 3 months apart after the Week 52/End of Study Visit. The following procedures were completed at the 3- and 6-month Post Treatment Follow-up Visits:

Document gout flares and intensity.

Record vital signs (blood pressure, respiratory rate, temperature, and heart rate) prior to discharge.

Perform a targeted physical examination (at a minimum this should include heart, lungs and abdominal examination).

Record weight.

Collect swollen/tender joint counts; administer HAQ; and record physician global assessments.

Digital photography of hands and feet.

Obtain blood samples for hematology and clinical chemistry analysis.

Obtain a blood sample (1 sample) for measurement of SUA.

Obtain blood samples for anti-PEG and anti-uricase IgG antibodies (3 Month Post Treatment Follow-up Visit only).

Inquire about AEs and concomitant medication use.

Populations for Analysis

The following analysis populations were defined for this study:

Intent-to-treat population (ITT): all randomized subjects

Modified intention-to-treat (mITT) population: all randomized subjects who receive at least 1 dose of pegloticase

Per-protocol population (PP): all randomized subjects who receive at least 1 dose of pegloticase, were taking the 15 mg dose of MTX or placebo for MTX at the time of first pegloticase dose, and had no major protocol deviations that would challenge the validity of the data

Pharmacokinetic (PK) population: all randomized subjects who receive at least one dose of pegloticase and had a post-pegloticase sample evaluable for PK analysis

Safety population: all randomized subjects who take at least one dose of blinded MTX or placebo for MTX

MTX population: all subjects who take at least one dose of MTX

The ITT and mITT populations were used for analysis of efficacy data; subjects were analyzed according to the treatment to which they were randomized. The PP population was used for analysis of select efficacy endpoints; subjects were analyzed according to the treatment received. The safety population was used for analysis of safety data; subjects were analyzed according to the treatment received. The MTX population was used for analysis of safety data during the Run-In period prior to randomization.

Efficacy Endpoint Analysis

Efficacy analyses were performed using the ITT and mITT populations, with select endpoints analyzed using the PP population. Continuous variables were summarized using descriptive statistics (number of subjects, mean, median, standard deviation, minimum, and maximum).

Categorical variables were summarized using frequencies and percentages. Unless otherwise specified, baseline was defined as the last non-missing observation prior to the first dose of MTX.

Primary and Secondary Endpoint Analysis

The primary analysis was conducted in the ITT population. The primary efficacy endpoint was the proportion of responders during Month 6. A responder was defined as a subject for whom the proportion of time that the SUA-time curve was <6 mg/dL during the analysis interval was at least 80%. The proportion of time that the SUA level was below 6 mg/dL was defined as the ratio of the time during which the SUA level remains below 6 mg/dL (using linear interpolation, if necessary) to the entire time interval during Month 6. A subject was declared a non-responder if the subject had 2 SUA levels >6 mg/dL at 2 consecutive study visits beginning with the Week 2 Visit prior to or during Month 6. Additionally, a subject who withdraws from study treatment for any reason other than the stopping rule after randomization and prior to or during Month 6 (for the primary endpoint) or Months 9 or 12 (for the secondary endpoints) was considered a non-responder at the time of withdrawal (and for all subsequent time points) if SUA values were not collected at the planned time points. Sensitivity analyses of the primary and secondary endpoints included data (if available) for subjects who discontinued treatment due to stopping rule and remained on study.

The analysis of the primary endpoint and the secondary responder endpoints assessed risk difference (difference in response proportions) in a stratified analysis. The analysis used Cochran-Mantel-Haenszel (CMH) weighting to estimate the common risk difference within strata and to estimate the standard error of the common risk difference. Stratification for the analysis used the same factor as was used to stratify randomization, presence of tophi (yes, no). The difference in response rates, comparing pegloticase with MTX vs. pegloticase with placebo for MTX, was estimated along with the corresponding 95% confidence interval (CI) and p-value.

Subjects with resolution of ≥1 tophi were subjects with an overall tophus response of complete response (i.e., complete response in at least one tophus and no evidence of progressive disease, see Section 9.5.1.6.1). The difference in the proportion of subjects with resolution of ≥1 tophi at Week 52 between pegloticase with MTX and pegloticase with placebo for MTX was tested with a chi-square test, and the difference in rates was estimated along with the corresponding 95% confidence interval (CI) and p-value.

To control the overall Type 1 error rate of the study, taking into consideration the one primary and 3 secondary endpoints, the endpoints were tested sequentially. For each endpoint, pegloticase with MTX was tested against pegloticase with placebo for MTX at the 0.05 level only if pegloticase with MTX was statistically significant for the endpoint preceding it in the prespecified order and 3 secondary endpoints, the endpoints were tested sequentially. For each endpoint, pegloticase with MTX was tested against pegloticase with placebo for MTX at either the 0.05 level only if pegloticase with MTX was statistically significant for the endpoint preceding it in the prespecified order.

Exploratory Endpoint Analysis

HAQ-DI score, HAQ pain and health scores, tophus size (longest axis), urate deposition volume, swollen/tender joint counts, physician global assessment score, and mean SUA were summarized at baseline and each visit with descriptive statistics. Changes from baseline for these parameters to each visit and overall were analyzed with a mixed model repeated measures (MMRM) analysis of covariance (ANCOVA) model with a term for baseline score, tophi presence at baseline (except for analyses of tophi), and factors of treatment group, visit, and visit by treatment group interaction.

The proportion of subjects achieving 20%, 50%, or 70% improvement based on gout chronic response criteria was defined as 20/50/70% improvement in 4 of the 5 components (TJC, SJC, HAQ pain, HAQ health, and tophus area). The proportion of subjects with improvement was summarized and the difference between treatment groups analyzed with a CMH test. P-values for exploratory endpoints were provided for descriptive purposes only, and treatment effects with corresponding two-sided 95% confidence intervals were provided.

Pharmacokinetic and Anti-Drug Antibody Analysis

Concentrations for pegloticase and MTX polyglutamate (as appropriate) were summarized using descriptive statistics for the PK population. Details were provided in a separate PK analysis plan. Incidence of anti-drug antibodies and titer levels were summarized.

Safety Analysis

Treatment-emergent AEs (TEAEs) during the MTX Tolerability Assessment Period and Run-In Period were defined as events with an onset date on or after the first dose of MTX through the first pegloticase infusion, or 30 days after the last dose of MTX for subjects who do not receive pegloticase. TEAEs during the Pegloticase+IMM Period were defined as events that occur after the start of the first pegloticase infusion through 30 days after the last dose of pegloticase and/or MTX or placebo for MTX (whichever was later). TEAEs that occur during the MTX Tolerability Assessment Period prior to randomization (Weeks −6 to −4) was summarized separately for the MTX population. TEAEs were summarized for the safety population separately for the Run-In Period (after randomization at Week −4 to Day 1) by treatment group (MTX and placebo for MTX) and the Pegloticase+IMM Period by treatment group (pegloticase with MTX and pegloticase with placebo for MTX), and overall (after randomization through 30 days after the last dose of treatment) by treatment group (MTX and placebo for MTX). AEs that occur more than 30 days after the last dose of pegloticase and/or MTX or placebo for MTX through the 6-month follow-up visit was also summarized.

The number and percentage of subjects experiencing AEs were summarized by system organ class and preferred term. Summaries by maximum severity and relationship to MTX and/or pegloticase was also provided. SAEs and AEs leading to discontinuation of MTX and/or pegloticase were presented by system organ class and preferred term.

The proportion of subjects with SAEs and each AESI was summarized by treatment group. A Fisher's exact test was performed to evaluate the difference in proportions between pegloticase with MTX vs. pegloticase with placebo for MTX. The proportion of subjects experiencing an SAE and each AESI was summarized for each treatment group, along with the treatment difference in proportions, corresponding 95% CI for the treatment difference and p-value.

Laboratory test results, including urine albumin:creatinine ratio, were summarized by study visit and change from baseline. Shift tables for laboratory parameters by Common Terminology Criteria for Adverse Events grade were presented. Laboratory test results were also classified relative to the normal reference range (normal, low, or high).

Vital signs, including blood pressure, respiratory rate, temperature, and heart rate, were summarized by study visit and change from baseline.

Prior and concomitant medications were summarized and/or included in the data listings.

Data for the MTX Tolerability Assessment Period, Run-in Period and Pegloticase+IMM Period were summarized separately, and for the Run-in and Pegloticase+IMM periods combined, where applicable.

Interim Analyses

An interim analysis was undertaken when all subjects reached the Week 24 visit. An independent DMC was convened to oversee and interpret this analysis to assess the primary endpoint of maintaining SUA <6 mg/dL at least 80% of the time during Month 6 (Weeks 20, 21, 22, 23 and 24) comparing pegloticase with MTX to pegloticase with placebo for MTX, as well as to assess the safety of the co-administration of pegloticase with MTX based on all accrued data at that time. The DMC recommended unblinding the Sponsor, stopping the study, or continuing without change at the time of the interim analysis, based on pre-defined criteria that were outlined in the DMC charter. In the event of a highly clinically compelling increase in response rates with pegloticase with MTX vs pegloticase with placebo for MTX, and in the absence of any unexpected safety findings, the Sponsor may become unblinded for full data analysis. Subjects would continue on study through Week 52, with investigators and subjects remaining blinded. Clear parameters to guide decision criteria were pre-specified in advance.

Upon all subjects reaching Week 52, a final analysis was completed in which the secondary endpoints were tested, including maintaining SUA <6 mg/dL at least 80% of the time during Month 9, maintaining SUA <6 mg/dL at least 80% of the time during Month 12, and proportion of subjects with complete resolution of at least one tophus by digital photography through Week 24. Additional safety data accrued would also be summarized.

Criteria would also established and pre-specified for the DMC to recommend study discontinuation due to futility or an unexpected safety risk. An interim analysis for futility may be completed earlier on the basis of the MIRROR Open-Label study results. At the futility analysis there was no opportunity to conclude a benefit of MTX and therefore there was no adjustment to the Type I error.

If none of the above scenarios were established, the study would continue, and the Sponsor would remain blinded until all subjects reach Week 52.

Sample Size and Power Considerations

The response rate during Month 6 on pegloticase 8 mg every 2 weeks was 43% for the phase 3 studies. A sample size of 135 subjects (90 subjects randomized to receive pegloticase with MTX, 45 subjects randomized to receive pegloticase with placebo for MTX) provides 88% power at the 2-sided alpha=0.05 level to detect a difference of 28% (71% response rate for pegloticase with MTX vs. 43% for pegloticase with placebo for MTX).

Example 11

Results from Open-Label Clinical Trial in Patients with Uncontrolled Gout

Adult patients with uncontrolled gout who were beginning pegloticase therapy were considered for enrollment in this ongoing multicenter, open-label, efficacy and safety study of pegloticase with MTX co-treatment (NCT03635957). Patients were administered oral MTX (15 mg/week) and folate (1 mg/day) 4 weeks prior to the first pegloticase infusion (Day 1) and throughout the pegloticase treatment period. Blood was drawn prior to each infusion to measure sUA level, monitor clinical parameters, and examine for ADA development. All patients followed typical IR prophylaxis protocols (fexofenadine one day before and the morning of each infusion and acetaminophen and IV corticosteroid the morning of each infusion). Patients also received gout flare prophylaxis with either NSAIDs, colchicine or prednisone initiated at least 1 week prior to Day 1. The primary study outcome was the proportion of responders, defined as sUA <6 mg/dL for at least 80% of the time during month 6 (weeks 20, 22, and 24). All analyses were performed on a modified intent-to-treat population, defined as patients who received ≥1 pegloticase infusion.

A total of 17 patients were screened and 14 patients (all men, average age: 49.3±8.7 years) were enrolled. Patient characteristics are provided in Table 2. On Day 1, mean sUA was 9.2±2.5 mg/dL and 12 of the 14 patients had visible tophi. At the 6 months timepoint, 11/14 (78.6%, 95%CI 49.2-95.3%) met the responder definition, with 3 patients discontinuing after meeting stopping rules (pre-infusion sUA values greater than 6 mg/dL at 2 consecutive scheduled visits). All patients tolerated MTX. One serious AE of bacterial sepsis occurred (unrelated to study drug, resolved). AEs that occurred in >1 patient were: diarrhea and upper respiratory tract infection in 3 patients each, nasopharyngitis, sinusitis, muscle strain, and hypertension in 2 patients each. Gout flares occurred in 10/14 (71.4%) patients. No new safety concerns were identified.

Results are provided in Tables 3-10. An increased proportion of patients maintained therapeutic response at 6 months when treated concomitantly with MTX and pegloticase (78.6%) when compared to the previously reported 42% using pegloticase alone. These results support and reflect the improved response rates demonstrated in two prior case series.

For the following tables, abbreviations as follows may apply: ITT=Intent-to-Treat, Max=Maximum, Min=Minimum, mITT=Modified Intent-to-Treat, SD=Standard Deviation, sUA=serum Uric Acid, IMM=Immunomodulator, MTX=Methotrexate, PK=Pharmacokinetic, CI=Confidence Interval, NE=Not Estimable, eCRF=electronic case report form.

Percentages were based on the number of subjects in each population. Month 6 includes pre-infusion and post-infusion sUA assessments at Week 20, pre-infusion and post-infusion sUA assessments at Week 22, pre-infusion assessments at Week 24, and pre-infusion unscheduled sUA assessments between Week 20 and Week 24. Local laboratory-reported pre-infusion sUA values were included only when the sUA result from the central laboratory at the same time point was unavailable.

[1] Treatment stopping Rule: Subjects with a sUA level >6 mg/dL at 2 consecutive scheduled study visits beginning with Week 2

[2] If the subject's proportion of hours that sUA was <6 mg/dL was greater than or equal to 80% the subject was called a responder.

Subjects meeting the stopping rule were counted as non-responders. If only one sUA result was collected during Month 6 period, response was based on the single value. A subject with the proportion of hours less than 80% was counted as non-responders.

Any other subject was counted as a non-responder if sUA values were not collected during the Month 6 period.

[3] Two-sided 95% Exact Clopper-Pearson confidence interval.

TABLE 2 Subject Disposition Overall Number of Subjects n (%) Screened 17 Screen Failures 3 Received MTX [1] 1 Did not receive MTX 2 ITT Population 15 mITT Population 14 PK Population 0 Entered the MTX Run-in Period 15 Completed the MTX Run-in Period 14 (93.3) Discontinued from MTX Run-in Period [1] 1 (6.7) Entered Pegloticase + IMM Period 14 (100) Completed Treatment [2] 3 (21.4) 24 Weeks (Amendment 1) 1 (7.1) 52 Weeks (Amendment 2) 2 (14.3) Discontinued Treatment [3] 5 Reasons for Discontinuation Adverse Events 0 Lack of Efficacy (sUA stopping criteria met) 3 (60.0) Unacceptable Risk to Patient 0 Subject refusal of additional therapy 2 (40.0) Study Terminated by Sponsor 0 Pregnancy 0 Death 0 Completed Study 4 (28.6) At Week 24 (Amendment 1) 1 (7.1) At Week 52 (Amendment 2) 3 (21.4) Discontinued Study 3 Reasons for Discontinuation Death 0 Lack of Efficacy (sUA stopping criteria met) [4] 3 (100) Lost to Follow-Up 0 Study Terminated by Sponsor 0 Withdrawal by Subject 0 Have 3 month follow-up 0 Have 6 month follow-up 0

TABLE 3 SUA < 6 mg/dL Responders during Month 3 and Overall (Months 3 and 6 Combined) (ITT and mITT Populations) ITT Population mITT Population Time Point N = 15 N = 14 Month 3 (Weeks 10, 12, 14) Responder, n (%) [2] 11 (73.3) 11 (78.6) 95% Clopper-Pearson Confidence Interval [3] 44.9, 92.2 49.2, 95.3 Non-Responder, n (%) 4 (26.7) 3 (21.4) Proportion of Time during Period that sUA < 6 mg/dL n 11 11 Mean (SD) 100.0 (0.00) 100.0 (0.00) Median  100.0  100.0 Min, Max 100, 100 100, 100 Month 3 (Weeks 10, 12, 14) Discontinued due to stopping rule prior to Week 14, n (%) [1] 3 (20.0) 3 (21.4) Subjects missing all data in analysis period, n (%) 3 (20.0) 2 (14.3) Subjects with only one measurement (above cutoff) in analysis period, n (%) 1 (6.7) 1 (7.1) Subjects with only one measurement (below cutoff) in analysis period, n (%)  0  0 Overall (Month 3 and Month 6 Responder, n (%) [2] 11 (73.3) 11 (78.6) Combined) [4] 95% Clopper-Pearson Confidence Interval [3] 44.9, 92.2 49.2, 95.3 Non-Responder, n (%) 4 (26.7) 3 (21.4) Overall (Month 3 and Month 6 Proportion of Time during Period that sUA < 6 mg/dL Combined) [4] n 11 11 Mean (SD) 100.0 (0.00) 100.0 (0.00) Median  100.0  100.0 Min, Max 100, 100 100, 100 Discontinued due to stopping rule prior to Week 14, n (%) [1] 3 (20.0) 3 (21.4)

TABLE 4 Serum Uric Acid < 5 mg/dL Responders during Month 3, Month 6, and Overall (Month 3 and Month 6 Combined) (ITT Population and mITT Population) ITT Population mITT Population Time Point N = 15 N = 14 Month 3 (Weeks 10, 12, 14) Responder, n (%) [2] 11 (73.3) 11 (78.6) 95% Clopper-Pearson Confidence Interval [3] 44.9, 92.2 49.2, 95.3 Non-Responder, n (%) 4 (26.7) 3 (21.4) Proportion of Time during Period that sUA < 5 mg/dL n 11 11 Mean (SD) 100.0 (0.00) 100.0 (0.00) Median  100.0  100.0 Min, Max 100, 100 100, 100 Month 3 (Weeks 10, 12, 14) Discontinued due to stopping rule prior to Week 14, n (%) [1] 3 (20.0) 3 (21.4) Subjects missing all data in analysis period, n (%) 3 (20.0) 2 (14.3) Subjects with only one measurement (above cutoff) in analysis period, n (%) 1 (6.7) 1 (7.1) Subjects with only one measurement (below cutoff) in analysis period, n (%)  0  0 Month 6 (Weeks 20, 22, 24) Responder, n (%) [2] 11 (73.3) 11 (78.6) 95% Clopper-Pearson Confidence Interval [3] 44.9, 92.2 49.2, 95.3 Non-Responder, n (%) 4 (26.7) 3 (21.4) Month 6 (Weeks 20, 22, 24) Proportion of Time during Period that sUA < 5 mg/dL n 11 11 Mean (SD) 100.0 (0.00) 100.0 (0.00) Median  100.0  100.0 Min, Max 100, 100 100, 100 Discontinued due to stopping rule prior to Week 24, n (%) [1] 3 (20.0) 3 (21.4) Subjects missing all data in analysis period, n (%) 4 (26.7) 3 (21.4) Subjects with only one measurement (above cutoff) in analysis period, n (%)  0  0 Subjects with only one measurement (below cutoff) in analysis period, n (%)  0  0 Overall (Month 3 and Month 6 Responder, n (%) [4] 11 (73.3) 11 (78.6) Combined) [4] 95% Clopper-Pearson Confidence Interval [3] 44.9, 92.2 49.2, 95.3 Non-Responder, n (%) 4 (26.7) 3 (21.4) Proportion of Time during Period that sUA < 5 mg/dL n 11 11 Mean (SD) 100.0 (0.00) 100.0 (0.00) Median  100.0  100.0 Min, Max 100, 100 100, 100 Discontinued due to stopping rule prior to Week 24, n (%) [1] 3 (20.0) 3 (21.4)

TABLE 5 Serum Uric Acid (mg/dL): Observed Values and Change from Methotrexate Baseline Values (mITT Population) Visit mITT Population (N = 14) Statistics Baseline [1] Observed Change from Baseline Baseline [2] n 14 Mean (SD) 8.91 (1.877) Median 9.05 Min, Max  5.4, 12.4 95% CI [3] (7.82, 9.99) sUA < 6 mg/dL, n (%)  1 (7.1%) Week -2 n 14 14 14 Mean (SD) 8.91 (1.877) 9.45 (2.211)  0.54 (0.839) Median 9.05 9.30 0.50 Min, Max 5.4, 12.4  5.2, 14.6 −0.9, 2.2 95% CI [3] (7.82, 9.99)   (8.17, 10.73)  (0.06, 1.03) sUA < 6 mg/dL, n (%)  1 (7.1%) Day 1 - Pre-Infusion n 14 14 14 Mean (SD) 8.91 (1.877) 9.16 (2.486)  0.25 (1.283) Median 9.05 9.00 −0.25 Min, Max 5.4, 12.4  4.7, 15.8 −1.2, 3.4 95% CI [3] (7.82, 9.99)   (7.72, 10.59) (−0.49, 0.99) sUA < 6 mg/dL, n (%)  1 (7.1%) Day 1 - Post-Infusion n 11 11 11 Mean (SD) 8.48 (1.758) 1.18 (1.417) −7.30 (2.081) Median 8.70 0.30 −7.30 Min, Max 5.4, 11.6 0.3, 4.9 −11.3, −3.8 95% CI [3] (7.30, 9.66)  (0.23, 2.13)  (−8.70, −5.90) sUA < 6 mg/dL, n (%)   11 (100%) Week 1 n 6 6 6 Mean (SD) 8.10 (1.541) 0.30 (0.000) −7.80 (1.541) Median 8.30 0.30 −8.00 Min, Max 5.4, 9.6  0.3, 0.3  −9.3, −5.1 95% CI [3] (6.48, 9.72)  (0.30, 0.30)  (−9.42, −6.18) sUA < 6 mg/dL, n (%)   6 (100%) Week 2 - Pre-Infusion n 14 14 14 Mean (SD) 8.91 (1.877) 1.26 (2.163) −7.65 (2.496) Median 9.05 0.30 −8.00 Min, Max 5.4, 12.4 0.3, 7.7 −11.3, −1.0 95% CI [3] (7.82, 9.99)  (0.01, 2.51)  (−9.09, −6.21) sUA < 6 mg/dL, n (%)  13 (92.9%) Week 2 - Post-Infusion n 14 14 14 Mean (SD) 8.91 (1.877) 0.30 (0.000) −8.61 (1.877) Median 9.05 0.30 −8.75 Min, Max 5.4, 12.4 0.3, 0.3 −12.1, −5.1 95% CI [3] (7.82, 9.99)  (0.30, 0.30)  (−9.69, −7.52) sUA < 6 mg/dL, n (%)   14 (100%) Week 4 - Pre-Infusion n 14 14 14 Mean (SD) 8.91 (1.877) 1.61 (2.637) −7.29 (3.137) Median 9.05 0.30 −7.45 Min, Max 5.4, 12.4 0.3, 8.2 −12.1, −0.5 95% CI [3] (7.82, 9.99)  (0.09, 3.14)  (−9.10, −5.48) sUA < 6 mg/dL, n (%)  12 (85.7%) Week 4 - Post-Infusion n 13 13 13 Mean (SD) 8.92 (1.953) 0.30 (0.000) −8.62 (1.953) Median 9.40 0.30 −9.10 Min, Max 5.4, 12.4 0.3, 0.3 −12.1, −5.1 95% CI [3] (7.74, 10.10) (0.30, 0.30)  (−9.80, −7.44) sUA < 6 mg/dL, n (%)   13 (100%) Week 6 - Pre-Infusion n 13 13 13 Mean (SD) 8.92 (1.953) 0.91 (2.191) −8.02 (2.779) Median 9.40 0.30 −8.40 Min, Max 5.4, 12.4 0.3, 8.2 −12.1, −1.4 95% CI [3] (7.74, 10.10) (0.00, 2.23)  (−9.69, −6.34) sUA < 6 mg/dL, n (%)  12 (92.3%) Week 6 - Post-Infusion n 12 12 12 Mean (SD) 8.87 (2.029) 0.30 (0.000) −8.57 (2.029) Median 9.05 0.30 −8.75 Min, Max 5.4, 12.4 0.3, 0.3 −12.1, −5.1 95% CI [3] (7.58, 10.16) (0.30, 0.30)  (−9.86, −7.28) sUA < 6 mg/dL, n (%)   12 (100%) Week 7 n 4 4 4 Mean (SD) 8.70 (2.960) 0.30 (0.000) −8.40 (2.960) Median 8.50 0.30 −8.20 Min, Max 5.4, 12.4 0.3, 0.3 −12.1, −5.1 95% CI [3] (3.99, 13.41) (0.30, 0.30) (−13.11, −3.69) sUA < 6 mg/dL, n (%)   4 (100%) Week 8 - Pre-Infusion n 12 12 12 Mean (SD) 8.87 (2.029) 1.08 (2.472) −7.79 (3.227) Median 9.05 0.30 −7.98 Min, Max 5.4, 12.4 0.3, 8.9 −12.1, 0.2  95% CI [3] (7.58, 10.16) (0.00, 2.65)  (−9.84, −5.74) sUA < 6 mg/dL, n (%)  11 (91.7%) Week 8 - Post-Infusion n 12 12 12 Mean (SD) 8.87 (2.029) 0.30 (0.000) −8.57 (2.029) Median 9.05 0.30 −8.75 Min, Max 5.4, 12.4 0.3, 0.3 −12.1, −5.1 95% CI [3] (7.58, 10.16) (0.30, 0.30)  (−9.86, −7.28) sUA < 6 mg/dL, n (%)   12 (100%) Week 10 - Pre-Infusion n 12 12 12 Mean (SD) 8.87 (2.029) 0.95 (2.252) −7.92 (3.069) Median 9.05 0.30 −8.35 Min, Max 5.4, 12.4 0.3, 8.1 −12.1, −0.6 95% CI [3] (7.58, 10.16) (0.00, 2.38)  (−9.87, −5.97) sUA < 6 mg/dL, n (%)  11 (91.7%) Week 10 - Post-Infusion n 11 11 11 Mean (SD) 8.88 (2.127) 0.30 (0.000) −8.58 (2.127) Median 9.40 0.30 −9.10 Min, Max 5.4, 12.4 0.3, 0.3 −12.1, −5.1 95% CI [3] (7.45, 10.31) (0.30, 0.30) (−10.01, −7.15) sUA < 6 mg/dL, n (%)   11 (100%) Week 12 - Pre-Infusion n 11 11 11 Mean (SD) 8.88 (2.127) 0.30 (0.015) −8.59 (2.124) Median 9.40 0.30 −9.10 Min, Max 5.4, 12.4 0.3, 0.3 −12.1, −5.1 95% CI [3] (7.45, 10.31) (0.29, 0.31) (−10.01, −7.16) sUA < 6 mg/dL, n (%)   11 (100%) Week 12 - Post-Infusion n 10 10 10 Mean (SD) 8.98 (2.216) 0.30 (0.000) −8.68 (2.216) Median 9.50 0.30 −9.20 Min, Max 5.4, 12.4 0.3, 0.3 −12.1, −5.1 95% CI [3] (7.40, 10.56) (0.30, 0.30) (−10.26, −7.10) sUA < 6 mg/dL, n (%)   10 (100%) Week 14 - Pre-Infusion n 11 11 11 Mean (SD) 8.88 (2.127) 0.30 (0.000) −8.58 (2.127) Median 9.40 0.30 −9.10 Min, Max 5.4, 12.4 0.3, 0.3 −12.1, −5.1 95% CI [3] (7.45, 10.31) (0.30, 0.30) (−10.01, −7.15) sUA < 6 mg/dL, n (%)   11 (100%) Week 14 - Post-Infusion n 10 10 10 Mean (SD) 8.80 (2.224) 0.30 (0.000) −8.50 (2.224) Median 8.65 0.30 −8.35 Min, Max 5.4, 12.4 0.3, 0.3 −12.1, −5.1 95% CI [3] (7.21, 10.39) (0.30, 0.30) (−10.09, −6.91) sUA < 6 mg/dL, n (%)   10 (100%) Week 16 - Pre-Infusion n 11 11 11 Mean (SD) 8.88 (2.127) 0.30 (0.000) −8.58 (2.127) Median 9.40 0.30 −9.10 Min, Max 5.4, 12.4 0.3, 0.3 −12.1, −5.1 95% CI [3] (7.45, 10.31) (0.30, 0.30) (−10.01, −7.15) sUA < 6 mg/dL, n (%)   11 (100%) Week 16 - Post-Infusion n 11 11 11 Mean (SD) 8.88 (2.127) 0.30 (0.000) −8.58 (2.127) Median 9.40 0.30 −9.10 Min, Max 5.4, 12.4 0.3, 0.3 −12.1, −5.1 95% CI [3] (7.45, 10.31) (0.30, 0.30) (−10.01, −7.15) sUA < 6 mg/dL, n (%)   11 (100%) Week 18 - Pre-Infusion n 11 11 11 Mean (SD) 8.88 (2.127) 0.30 (0.000) −8.58 (2.127) Median 9.40 0.30 −9.10 Min, Max 5.4, 12.4 0.3, 0.3 −12.1, −5.1 95% CI [3] (7.45, 10.31) (0.30, 0.30) (−10.01, −7.15) sUA < 6 mg/dL, n (%)   11 (100%) Week 18 - Post-Infusion n 11 11 11 Mean (SD) 8.88 (2.127) 0.30 (0.000) −8.58 (2.127) Median 9.40 0.30 −9.10 Min, Max 5.4, 12.4 0.3, 0.3 −12.1, −5.1 95% CI [3] (7.45, 10.31) (0.30, 0.30) (−10.01, −7.15) sUA < 6 mg/dL, n (%)   11 (100%) Week 20 - Pre-Infusion n 11 11 11 Mean (SD) 8.88 (2.127) 0.30 (0.000) −8.58 (2.127) Median 9.40 0.30 −9.10 Min, Max 5.4, 12.4 0.3, 0.3 −12.1, −5.1 95% CI [3] (7.45, 10.31) (0.30, 0.30) (−10.01, −7.15) sUA < 6 mg/dL, n (%)   11 (100%) Week 20 - Post-Infusion n 11 11 11 Mean (SD) 8.88 (2.127) 0.30 (0.000) −8.58 (2.127) Median 9.40 0.30 −9.10 Min, Max 5.4, 12.4 0.3, 0.3 −12.1, −5.1 95% CI [3] (7.45, 10.31) (0.30, 0.30) (−10.01, −7.15) sUA < 6 mg/dL, n (%)   11 (100%) Week 22 - Pre-Infusion n 11 11 11 Mean (SD) 8.88 (2.127) 0.30 (0.000) −8.58 (2.127) Median 9.40 0.30 −9.10 Min, Max 5.4, 12.4 0.3, 0.3 −12.1, −5.1 95% CI [3] (7.45, 10.31) (0.30, 0.30) (−10.01, −7.15) sUA < 6 mg/dL, n (%)   11 (100%) Week 22 - Post-Infusion n 11 11 11 Mean (SD) 8.88 (2.127) 0.30 (0.000) −8.58 (2.127) Median 9.40 0.30 −9.10 Min, Max 5.4, 12.4 0.3, 0.3 −12.1, −5.1 95% CI [3] (7.45, 10.31) (0.30, 0.30) (−10.01, −7.15) sUA < 6 mg/dL, n (%)   11 (100%) Week 24 - Pre-Infusion n 11 11 11 Mean (SD) 8.88 (2.127) 0.30 (0.000) −8.58 (2.127) Median 9.40 0.30 −9.10 Min, Max 5.4, 12.4 0.3, 0.3 −12.1, −5.1 95% CI [3] (7.45, 10.31) (0.30, 0.30) (−10.01, −7.15) sUA < 6 mg/dL, n (%)   11 (100%) Week 24 - Post-Infusion n 5 5 5 Mean (SD) 9.02 (2.648) 0.30 (0.000) −8.72 (2.648) Median 9.60 0.30 −9.30 Min, Max 5.4, 12.4 0.3, 0.3 −12.1, −5.1 95% CI [3] (5.73, 12.31) (0.30, 0.30) (−12.01, −5.43) sUA < 6 mg/dL, n (%)   5 (100%) Week 26 - Pre-Infusion n 8 8 8 Mean (SD) 9.10 (2.449) 0.30 (0.000) −8.80 (2.449) Median 9.65 0.30 −9.35 Min, Max 5.4, 12.4 0.3, 0.3 −12.1, −5.1 95% CI [3] (7.05, 11.15) (0.30, 0.30) (−10.85, −6.75) sUA < 6 mg/dL, n (%)   8 (100%) Week 28 - Pre-Infusion n 8 8 8 Mean (SD) 9.10 (2.449) 0.30 (0.000) −8.80 (2.449) Median 9.65 0.30 −9.35 Min, Max 5.4, 12.4 0.3, 0.3 −12.1, −5.1 95% CI [3] (7.05, 11.15) (0.30, 0.30) (−10.85, −6.75) sUA < 6 mg/dL, n (%)   8 (100%) Week 30 - Pre-Infusion n 8 8 8 Mean (SD) 9.10 (2.449) 0.30 (0.000) −8.80 (2.449) Median 9.65 0.30 −9.35 Min, Max 5.4, 12.4 0.3, 0.3 −12.1, −5.1 95% CI [3] (7.05, 11.15) (0.30, 0.30) (−10.85, −6.75) sUA < 6 mg/dL, n (%)   8 (100%) Week 32 - Pre-Infusion n 10 10 10 Mean (SD) 8.83 (2.235) 0.30 (0.000) −8.53 (2.235) Median 8.75 0.30 −8.45 Min, Max 5.4, 12.4 0.3, 0.3 −12.1, −5.1 95% CI [3] (7.23, 10.43) (0.30, 0.30) (−10.13, −6.93) sUA < 6 mg/dL, n (%)   10 (100%) Week 32 - Post-Infusion n 8 8 8 Mean (SD) 9.10 (2.449) 0.30 (0.000) −8.80 (2.449) Median 9.65 0.30 −9.35 Min, Max 5.4, 12.4 0.3, 0.3 −12.1, −5.1 95% CI [3] (7.05, 11.15) (0.30, 0.30) (−10.85, −6.75) sUA < 6 mg/dL, n (%)   8 (100%) Week 34 - Pre-Infusion n 10 10 10 Mean (SD) 8.83 (2.235) 0.82 (1.046) −8.01 (2.709) Median 8.75 0.30 −8.20 Min, Max 5.4, 12.4 0.3, 2.9 −12.1, −4.9 95% CI [3] (7.23, 10.43) (0.07, 1.57) (−9.95, −6.07) sUA < 6 mg/dL, n (%)   10 (100%) Week 34 - Post-Infusion n 8 8 8 Mean (SD) 9.10 (2.449) 0.30 (0.000) −8.80 (2.449) Median 9.65 0.30 −9.35 Min, Max 5.4, 12.4 0.3, 0.3 −12.1, −5.1 95% CI [3] (7.05, 11.15) (0.30, 0.30) (−10.85, −6.75) sUA < 6 mg/dL, n (%)   8 (100%) Week 36 - Pre-Infusion n 9 9 9 Mean (SD) 9.10 (2.190) 1.58 (2.425) −7.52 (3.769) Median 9.60 0.30 −9.14 Min, Max 5.4, 12.4 0.1, 6.4 −12.1, −1.2 95% CI [3] (7.42, 10.78) (0.00, 3.44) (−10.42, −4.63) sUA < 6 mg/dL, n (%)   8 (88.9%) Week 36 - Post-Infusion n 6 6 6 Mean (SD) 9.38 (2.577) 0.30 (0.000) −9.08 (2.577) Median 9.65 0.30 −9.35 Min, Max 5.4, 12.4 0.3, 0.3 −12.1, −5.1 95% CI [3] (6.68, 12.09) (0.30, 0.30) (−11.79, −6.38) sUA < 6 mg/dL, n (%)   6 (100%) Week 38 - Pre-Infusion n 5 5 5 Mean (SD) 8.94 (2.613) 0.93 (1.583) −8.01 (3.904) Median 9.60 0.30 −9.30 Min, Max 5.4, 12.4 0.0, 3.8 −12.1, −1.6 95% CI [3] (5.70, 12.18) (0.00, 2.90) (−12.86, −3.16) sUA < 6 mg/dL, n (%)   5 (100%) Week 40 - Pre-Infusion n 3 3 3 Mean (SD) 10.57 (1.589)  0.30 (0.000) −10.27 (1.589)  Median 9.70 0.30 −9.40 Min, Max 9.6, 12.4 0.3, 0.3 −12.1, −9.3 95% CI [3] (6.62, 14.51) (0.30, 0.30) (−14.21, −6.32) sUA < 6 mg/dL, n (%)   3 (100%) Week 42 - Pre-Infusion n 3 3 3 Mean (SD) 10.57 (1.589)  0.30 (0.000) −10.27 (1.589)  Median 9.70 0.30 −9.40 Min, Max 9.6, 12.4 0.3, 0.3 −12.1, −9.3 95% CI [3] (6.62, 14.51) (0.30, 0.30) (−14.21, −6.32) sUA < 6 mg/dL, n (%)   3 (100%) Week 44 - Pre-Infusion n 3 3 3 Mean (SD) 10.57 (1.589)  1.05 (1.305) −9.51 (2.487) Median 9.70 0.30 −9.30 Min, Max 9.6, 12.4 0.3, 2.6 −12.1, −7.1 95% CI [3] (6.62, 14.51) (0.00, 4.29) (−15.69, −3.34) sUA < 6 mg/dL, n (%)   3 (100%) Week 46 - Pre-Infusion n 2 2 2 Mean (SD) 11.00 (1.980)  0.30 (0.000) −10.70 (1.980)  Median 11.00 0.30 −10.70 Min, Max 9.6, 12.4 0.3, 0.3 −12.1, −9.3 95% CI [3] (0.00, 28.79) (0.30, 0.30) (−28.49, 7.09)  sUA < 6 mg/dL, n (%)   2 (100%) Week 48 - Pre-Infusion n 2 2 2 Mean (SD) 11.00 (1.980)  0.30 (0.000) −10.70 (1.980)  Median 11.00 0.30 −10.70 Min, Max 9.6, 12.4 0.3, 0.3 −12.1, −9.3 95% CI [3] (0.00, 28.79) (0.30, 0.30) (−28.49, 7.09)  sUA < 6 mg/dL, n (%)   2 (100%) Week 48 - Post-Infusion n 3 3 3 Mean (SD) 9.87 (2.411) 1.60 (2.252) −8.27 (4.441) Median 9.60 0.30 −9.30 Min, Max 7.6, 12.4 0.3, 4.2 −12.1, −3.4 95% CI [3] (3.88, 15.86) (0.00, 7.19) (−19.30, 2.77)  sUA < 6 mg/dL, n (%)   3 (100%) Week 50 - Pre-Infusion n 2 2 2 Mean (SD) 11.00 (1.980)  0.30 (0.000) −10.70 (1.980)  Median 11.00 0.30 −10.70 Min, Max 9.6, 12.4 0.3, 0.3 −12.1, −9.3 95% CI [3] (0.00, 28.79) (0.30, 0.30) (−28.49, 7.09)  sUA < 6 mg/dL, n (%)   2 (100%) Week 50 - Post-Infusion n 3 3 3 Mean (SD) 9.87 (2.411) 1.37 (1.848) −8.50 (4.060) Median 9.60 0.30 −9.30 Min, Max 7.6, 12.4 0.3, 3.5 −12.1, −4.1 95% CI [3] (3.88, 15.86) (0.00, 5.96) (−18.58, 1.58)  sUA < 6 mg/dL, n (%)   3 (100%) Week 52/ET n 2 2 2 Mean (SD) 11.00 (1.980)  0.30 (0.000) −10.70 (1.980)  Median 11.00 0.30 −10.70 Min, Max 9.6, 12.4 0.3, 0.3 −12.1, −9.3 95% CI [3] (0.00, 28.79) (0.30, 0.30) (−28.49, 7.09)  sUA < 6 mg/dL, n (%)   2 (100%) End of Pegloticase Infusions Visit n 2 2 2 Mean (SD) 7.75 (0.212) 0.30 (0.000) −7.45 (0.212) Median 7.75 0.30 −7.45 Min, Max 7.6, 7.9  0.3, 0.3  −7.6, −7.3 95% CI [3] (5.84, 9.66)  (0.30, 0.30)  (−9.36, −5.54) sUA < 6 mg/dL, n (%)   2 (100%) Early Termination Visit n 3 3 3 Mean (SD) 9.00 (0.520) 8.17 (0.058) −0.83 (0.493) Median 8.70 8.20 −0.60 Min, Max 8.7, 9.6  8.1, 8.2  −1.4, −0.5 95% CI [3] (7.71, 10.29) (8.02, 8.31) (−2.06, 0.39) sUA < 6 mg/dL, n (%) 0

TABLE 6 Serum Uric Acid (mg/dL): Observed Values and Change from Pegloticase Baseline Values (mITT Population) Visit mITT Population (N = 14) Statistics Baseline [1] Observed Change from Baseline Baseline [2] n 14 Mean (SD) 9.16 (2.486) Median 9.00 Min, Max  4.7, 15.8 95% CI [3]  (7.72, 10.59) sUA < 6 mg/dL, n (%)  1 (7.1%) Day 1 - Post-Infusion n 11 11 11 Mean (SD) 8.47 (1.736) 1.18 (1.417) −7.29 (2.254) Median 8.40 0.30 −7.30 Min, Max 4.7, 11.4 0.3, 4.9 −11.1, −3.5  95% CI [3] (7.31, 9.64)  (0.23, 2.13) (−8.80, −5.78) sUA < 6 mg/dL, n (%)   11 (100%) Week 1 n 6 6 6 Mean (SD) 7.58 (1.556) 0.30 (0.000) −7.28 (1.556) Median 8.05 0.30 −7.75 Min, Max 4.7, 9.1  0.3, 0.3 −8.8, −4.4 95% CI [3] (5.95, 9.22)  (0.30, 0.30) (−8.92, −5.65) sUA < 6 mg/dL, n (%)   6 (100%) Week 2 - Pre-Infusion n 14 14 14 Mean (SD) 9.16 (2.486) 1.26 (2.163) −7.90 (2.878) Median 9.00 0.30 −8.70 Min, Max 4.7, 15.8 0.3, 7.7 −11.9, −0.7  95% CI [3] (7.72, 10.59) (0.01, 2.51) (−9.56, −6.24) sUA < 6 mg/dL, n (%)  13 (92.9%) Week 2 - Post-Infusion n 14 14 14 Mean (SD) 9.16 (2.486) 0.30 (0.000) −8.86 (2.486) Median 9.00 0.30 −8.70 Min, Max 4.7, 15.8 0.3, 0.3 −15.5, −4.4  95% CI [3] (7.72, 10.59) (0.30, 0.30) (−10.29, −7.42)  sUA < 6 mg/dL, n (%)   14 (100%) Week 4 - Pre-Infusion n 14 14 14 Mean (SD) 9.16 (2.486) 1.61 (2.637) −7.54 (3.768) Median 9.00 0.30 −8.00 Min, Max 4.7, 15.8 0.3, 8.2 −15.5, −0.2  95% CI [3] (7.72, 10.59) (0.09, 3.14) (−9.72, −5.37) sUA < 6 mg/dL, η (%)  12 (85.7%) Week 4 - Post-Infusion n 13 13 13 Mean (SD) 9.22 (2.577) 0.30 (0.000) −8.92 (2.577) Median 9.10 0.30 −8.80 Min, Max 4.7, 15.8 0.3, 0.3 −15.5, −4.4  95% CI [3] (7.66, 10.77) (0.30, 0.30) (−10.47, −7.36)  sUA < 6 mg/dL, n (%)   13 (100%) Week 6 - Pre-Infusion n 13 13 13 Mean (SD) 9.22 (2.577) 0.91 (2.191) −8.31 (3.538) Median 9.10 0.30 −8.80 Min, Max 4.7, 15.8 0.3, 8.2 −15.5, −0.2  95% CI [3] (7.66, 10.77) (0.00, 2.23) (−10.45, −6.17)  sUA < 6 mg/dL, n (%)  12 (92.3%) Week 6 - Post-Infusion n 12 12 12 Mean (SD) 9.28 (2.679) 0.30 (0.000) −8.98 (2.679) Median 9.25 0.30 −8.95 Min, Max 4.7, 15.8 0.3, 0.3 −15.5, −4.4 95% CI [3] (7.58, 10.99) (0.30, 0.30) (−10.69, −7.28) sUA < 6 mg/dL, n (%)   12 (100%) Week 7 n 4 4 4 Mean (SD) 9.20 (4.755) 0.30 (0.000) −8.90 (4.755) Median 8.15 0.30 −7.85 Min, Max 4.7, 15.8 0.3, 0.3 −15.5, −4.4 95% CI [3] (1.63, 16.77) (0.30, 0.30) (−16.47, −1.33) sUA < 6 mg/dL, n (%)   4 (100%) Week 8 - Pre-Infusion n 12 12 12 Mean (SD) 9.28 (2.679) 1.08 (2.472) −8.20 (3.624) Median 9.25 0.30 −8.33 Min, Max 4.7, 15.8 0.3, 8.9 −15.5, −0.5 95% CI [3] (7.58, 10.99) (0.00, 2.65) (−10.51, −5.90) sUA < 6 mg/dL, n (%)  11 (91.7%) Week 8 - Post-Infusion n 12 12 12 Mean (SD) 9.28 (2.679) 0.30 (0.000) −8.98 (2.679) Median 9.25 0.30 −8.95 Min, Max 4.7, 15.8 0.3, 0.3 −15.5, −4.4 95% CI [3] (7.58, 10.99) (0.30, 0.30) (−10.69, −7.28) sUA < 6 mg/dL, n (%)   12 (100%) Week 10 - Pre-Infusion n 12 12 12 Mean (SD) 9.28 (2.679) 0.95 (2.252) −8.33 (3.476) Median 9.25 0.30 −8.70 Min, Max 4.7, 15.8 0.3, 8.1 −15.5, −1.3 95% CI [3] (7.58, 10.99) (0.00, 2.38) (−10.54, −6.12) sUA < 6 mg/dL, n (%)   11 (91.7%) Week 10 - Post-Infusion n 11 11 11 Mean (SD) 9.27 (2.810) 0.30 (0.000) −8.97 (2.810) Median 9.10 0.30 −8.80 Min, Max 4.7, 15.8 0.3, 0.3 −15.5, −4.4 95% CI [3] (7.38, 11.16) (0.30, 0.30) (−10.86, −7.08) sUA < 6 mg/dL, n (%)   11 (100%) Week 12 - Pre-Infusion n 11 11 11 Mean (SD) 9.27 (2.810) 0.30 (0.015) −8.98 (2.806) Median 9.10 0.30 −8.80 Min, Max 4.7, 15.8 0.3, 0.3 −15.5, −4.4 95% CI [3] (7.38, 11.16) (0.29, 0.31) (−10.86, −7.09) sUA < 6 mg/dL, n (%)   11 (100%) Week 12 - Post-Infusion n 10 10 10 Mean (SD) 9.43 (2.911) 0.30 (0.000) −9.13 (2.911) Median 9.35 0.30 −9.05 Min, Max 4.7, 15.8 0.3, 0.3 −15.5, −4.4 95% CI [3] (7.35, 11.51) (0.30, 0.30) (−11.21, −7.05) sUA < 6 mg/dL, n (%)   10 (100%) Week 14 - Pre-Infusion n 11 11 11 Mean (SD) 9.27 (2.810) 0.30 (0.000) −8.97 (2.810) Median 9.10 0.30 −8.80 Min, Max 4.7, 15.8 0.3, 0.3 −15.5, −4.4 95% CI [3] (7.38, 11.16) (0.30, 0.30) (−10.86, −7.08) sUA < 6 mg/dL, n (%)   11 (100%) Week 14 - Post-Infusion n 10 10 10 Mean (SD) 9.31 (2.959) 0.30 (0.000) −9.01 (2.959) Median 9.35 0.30 −9.05 Min, Max 4.7, 15.8 0.3, 0.3 −15.5, −4.4 95% CI [3] (7.19, 11.43) (0.30, 0.30) (−11.13, −6.89) sUA < 6 mg/dL, n (%)   10 (100%) Week 16 - Pre-Infusion n 11 11 11 Mean (SD) 9.27 (2.810) 0.30 (0.000) −8.97 (2.810) Median 9.10 0.30 −8.80 Min, Max 4.7, 15.8 0.3, 0.3 −15.5, −4.4 95% CI [3] (7.38, 11.16) (0.30, 0.30) (−10.86, −7.08) sUA < 6 mg/dL, n (%)   11 (100%) Week 16 - Post-Infusion n 11 11 11 Mean (SD) 9.27 (2.810) 0.30 (0.000) −8.97 (2.810) Median 9.10 0.30 −8.80 Min, Max 4.7, 15.8 0.3, 0.3 −15.5, −4.4 95% CI [3] (7.38, 11.16) (0.30, 0.30) (−10.86, −7.08) sUA < 6 mg/dL, n (%)   11 (100%) Week 18 - Pre-Infusion n 11 11 11 Mean (SD) 9.27 (2.810) 0.30 (0.000) −8.97 (2.810) Median 9.10 0.30 −8.80 Min, Max 4.7, 15.8 0.3, 0.3 −15.5, −4.4 95% CI [3] (7.38, 11.16) (0.30, 0.30) (−10.86, −7.08) sUA < 6 mg/dL, n (%)   11 (100%) Week 18 - Post-Infusion n 11 11 11 Mean (SD) 9.27 (2.810) 0.30 (0.000) −8.97 (2.810) Median 9.10 0.30 −8.80 Min, Max 4.7, 15.8 0.3, 0.3 −15.5, −4.4 95% CI [3] (7.38, 11.16) (0.30, 0.30) (−10.86, −7.08) sUA < 6 mg/dL, n (%)   11 (100%) Week 20 - Pre-Infusion n 11 11 11 Mean (SD) 9.27 (2.810) 0.30 (0.000) −8.97 (2.810) Median 9.10 0.30 −8.80 Min, Max 4.7, 15.8 0.3, 0.3 −15.5, −4.4 95% CI [3] (7.38, 11.16) (0.30, 0.30) (−10.86, −7.08) sUA < 6 mg/dL, n (%)   11 (100%) Week 20 - Post-Infusion n 11 11 11 Mean (SD) 9.27 (2.810) 0.30 (0.000) −8.97 (2.810) Median 9.10 0.30 −8.80 Min, Max 4.7, 15.8 0.3, 0.3 −15.5, −4.4 95% CI [3] (7.38, 11.16) (0.30, 0.30) (−10.86, −7.08) sUA < 6 mg/dL, n (%)   11 (100%) Week 22 - Pre-Infusion n 11 11 11 Mean (SD) 9.27 (2.810) 0.30 (0.000) −8.97 (2.810) Median 9.10 0.30 −8.80 Min, Max 4.7, 15.8 0.3, 0.3 −15.5, −4.4 95% CI [3] (7.38, 11.16) (0.30, 0.30) (−10.86, −7.08) sUA < 6 mg/dL, n (%)   11 (100%) Week 22 - Post-Infusion n 11 11 11 Mean (SD) 9.27 (2.810) 0.30 (0.000) −8.97 (2.810) Median 9.10 0.30 −8.80 Min, Max 4.7, 15.8 0.3, 0.3 −15.5, −4.4 95% CI [3] (7.38, 11.16) (0.30, 0.30) (−10.86, −7.08) sUA < 6 mg/dL, n (%)   11 (100%) Week 24 - Pre-Infusion n 11 11 11 Mean (SD) 9.27 (2.810) 0.30 (0.000) −8.97 (2.810) Median 9.10 0.30 −8.80 Min, Max 4.7, 15.8 0.3, 0.3 −15.5, −4.4 95% CI [3] (7.38, 11.16) (0.30, 0.30) (−10.86, −7.08) sUA < 6 mg/dL, n (%)   11 (100%) Week 24 - Post-Infusion n 5 5 5 Mean (SD) 9.48 (4.135) 0.30 (0.000) −9.18 (4.135) Median 9.60 0.30 −9.30 Min, Max 4.7, 15.8 0.3, 0.3 −15.5, −4.4 95% CI [3] (4.35, 14.61) (0.30, 0.30) (−14.31, −4.05) sUA < 6 mg/dL, n (%)   5 (100%) Week 26 - Pre-Infusion n 8 8 8 Mean (SD) 9.41 (3.293) 0.30 (0.000) −9.11 (3.293) Median 9.25 0.30 −8.95 Min, Max 4.7, 15.8 0.3, 0.3 −15.5, −4.4 95% CI [3] (6.66, 12.17) (0.30, 0.30) (−11.87, −6.36) sUA < 6 mg/dL, n (%)   8 (100%) Week 28 - Pre-Infusion n 8 8 8 Mean (SD) 9.41 (3.293) 0.30 (0.000) −9.11 (3.293) Median 9.25 0.30 −8.95 Min, Max 4.7, 15.8 0.3, 0.3 −15.5, −4.4 95% CI [3] (6.66, 12.17) (0.30, 0.30) (−11.87, −6.36) sUA < 6 mg/dL, n (%)   8 (100%) Week 30 - Pre-Infusion n 8 8 8 Mean (SD) 9.41 (3.293) 0.30 (0.000) −9.11 (3.293) Median 9.25 0.30 −8.95 Min, Max 4.7, 15.8 0.3, 0.3 −15.5, −4.4 95% CI [3] (6.66, 12.17) (0.30, 0.30) (−11.87, −6.36) sUA < 6 mg/dL, n (%)   8 (100%) Week 32 - Pre-Infusion n 10 10 10 Mean (SD) 9.29 (2.961) 0.30 (0.000) −8.99 (2.961) Median 9.25 0.30 −8.95 Min, Max 4.7, 15.8 0.3, 0.3 −15.5, −4.4 95% CI [3] (7.17, 11.41) (0.30, 0.30) (−11.11, −6.87) sUA < 6 mg/dL, n (%)   10 (100%) Week 32 - Post-Infusion n 8 8 8 Mean (SD) 9.41 (3.293) 0.30 (0.000) −9.11 (3.293) Median 9.25 0.30 −8.95 Min, Max 4.7, 15.8 0.3, 0.3 −15.5, −4.4 95% CI [3] (6.66, 12.17) (0.30, 0.30) (−11.87, −6.36) sUA < 6 mg/dL, n (%)   8 (100%) Week 34 - Pre-Infusion n 10 10 10 Mean (SD) 9.29 (2.961) 0.82 (1.046) −8.47 (3.248) Median 9.25 0.30 −7.95 Min, Max 4.7, 15.8 0.3, 2.9 −15.5, −4.4 95% CI [3] (7.17, 11.41) (0.07, 1.57) (−10.79, −6.15) sUA < 6 mg/dL, n (%)   10 (100%) Week 34 - Post-Infusion n 8 8 8 Mean (SD) 9.41 (3.293) 0.30 (0.000) −9.11 (3.293) Median 9.25 0.30 −8.95 Min, Max 4.7, 15.8 0.3, 0.3 −15.5, −4.4 95% CI [3] (6.66, 12.17) (0.30, 0.30) (−11.87, −6.36) sUA < 6 mg/dL, n (%)   8 (100%) Week 36 - Pre-Infusion n 9 9 9 Mean (SD) 9.48 (3.077) 1.58 (2.425) −7.90 (4.094) Median 9.60 0.30 −8.60 Min, Max 4.7, 15.8 0.1, 6.4 −15.5, −2.5 95% CI [3] (7.11, 11.84) (0.00, 3.44) (−11.05, −4.75) sUA < 6 mg/dL, n (%)   8 (88.9%) Week 36 - Post-Infusion n 6 6 6 Mean (SD) 9.68 (3.799) 0.30 (0.000) −9.38 (3.799) Median 9.50 0.30 −9.20 Min, Max 4.7, 15.8 0.3, 0.3 −15.5, −4.4 95% CI [3] (5.70, 13.67) (0.30, 0.30) (−13.37, −5.40) sUA < 6 mg/dL, n (%)   6 (100%) Week 38 - Pre-Infusion n 5 5 5 Mean (SD) 9.34 (4.142) 0.93 (1.583) −8.41 (5.229) Median 8.90 0.30 −8.60 Min, Max 4.7, 15.8 0.0, 3.8 −15.5, −0.9 95% CI [3] (4.20, 14.48) (0.00, 2.90) (−14.90, −1.92) sUA < 6 mg/dL, n (%)   5 (100%) Week 40 - Pre-Infusion n 3 3 3 Mean (SD) 11.60 (3.686)  0.30 (0.000) −11.30 (3.686)  Median 10.10 0.30 −9.80 Min, Max 8.9, 15.8 0.3, 0.3 −15.5, −8.6 95% CI [3] (2.44, 20.76) (0.30, 0.30) (−20.46, −2.14) sUA < 6 mg/dL, n (%)   3 (100%) Week 42 - Pre-Infusion n 3 3 3 Mean (SD) 11.60 (3.686)  0.30 (0.000) −11.30 (3.686)  Median 10.10 0.30 −9.80 Min, Max 8.9, 15.8 0.3, 0.3 −15.5, −8.6 95% CI [3] (2.44, 20.76) (0.30, 0.30) (−20.46, −2.14) sUA < 6 mg/dL, n (%)   3 (100%) Week 44 - Pre-Infusion n 3 3 3 Mean (SD) 11.60 (3.686)  1.05 (1.305) −10.55 (4.625)  Median 10.10 0.30 −9.80 Min, Max 8.9, 15.8 0.3, 2.6 −15.5, −6.3 95% CI [3] (2.44, 20.76) (0.00, 4.29) (−22.04, 0.94)  sUA < 6 mg/dL, n (%)   3 (100%) Week 46 - Pre-Infusion n 2 2 2 Mean (SD) 12.95 (4.031)  0.30 (0.000) −12.65 (4.031)  Median 12.95 0.30 −12.65 Min, Max 10.1, 15.8  0.3, 0.3 −15.5, −9.8 95% CI [3] (0.00, 49.16) (0.30, 0.30) (−48.86, 23.56) sUA < 6 mg/dL, n (%)   2 (100%) Week 48 - Pre-Infusion n 2 2 2 Mean (SD) 12.95 (4.031)  0.30 (0.000) −12.65 (4.031)  Median 12.95 0.30 −12.65 Min, Max 10.1, 15.8  0.3, 0.3 −15.5, −9.8 95% CI [3] (0.00, 49.16) (0.30, 0.30) (−48.86, 23.56) sUA < 6 mg/dL, n (%)   2 (100%) Week 48 - Post-Infusion n 3 3 3 Mean (SD) 11.93 (3.350)  1.60 (2.252) −10.33 (4.922)  Median 10.10 0.30 −9.80 Min, Max 9.9, 15.8 0.3, 4.2 −15.5, −5.7 95% CI [3] (3.61, 20.26) (0.00, 7.19) (−22.56, 1.89)  sUA < 6 mg/dL, n (%)   3 (100%) Week 50 - Pre-Infusion n 2 2 2 Mean (SD) 12.95 (4.031)  0.30 (0.000) −12.65 (4.031)  Median 12.95 0.30 −12.65 Min, Max 10.1, 15.8  0.3, 0.3 −15.5, −9.8 95% CI [3] (0.00, 49.16) (0.30, 0.30) (−48.86, 23.56) sUA < 6 mg/dL, n (%)   2 (100%) Week 50 - Post-Infusion n 3 3 3 Mean (SD) 11.93 (3.350)  1.37 (1.848) −10.57 (4.598)  Median 10.10 0.30 −9.80 Min, Max 9.9, 15.8 0.3, 3.5 −15.5, −6.4 95% CI [3] (3.61, 20.26) (0.00, 5.96) (−21.99, 0.86)  sUA < 6 mg/dL, n (%)   3 (100%) Week 52/ET n 2 2 2 Mean (SD) 12.95 (4.031)  0.30 (0.000) −12.65 (4.031)  Median 12.95 0.30 −12.65 Min, Max 10.1, 15.8  0.3, 0.3 −15.5, −9.8 95% CI [3] (0.00, 49.16) (0.30, 0.30) (−48.86, 23.56) sUA < 6 mg/dL, n (%)   2 (100%) End of Pegloticase Infusions Visit n 2 2 2 Mean (SD) 8.80 (1.556) 0.30 (0.000) −8.50 (1.556) Median 8.80 0.30 −8.50 Min, Max 7.7, 9.9  0.3, 0.3  −9.6, −7.4 95% CI [3] (0.00, 22.78) (0.30, 0.30) (−22.48, 5.48)  sUA < 6 mg/dL, n (%)   2 (100%) Early Termination Visit n 3 3 3 Mean (SD) 8.73 (0.577) 8.17 (0.058) −0.57 (0.635) Median 8.40 8.20 −0.20 Min, Max 8.4, 9.4  8.1, 8.2  −1.3, −0.2 95% CI [3] (7.30, 10.17) (8.02, 8.31) (−2.14, 1.01) sUA < 6 mg/dL, n (%) 0

TABLE 7 Serum Uric Acid (mg/dL): Observed Values and Change from Pegloticase Baseline Values by Month 6 sUA Responder Subgroup (mITT Population) Month 6 sUA Responders [1] (N = 11) Month 6 sUA Non-Responders [1] (N = 3) Visit Change from Change Statistics Baseline [2] Observed Baseline Baseline [2] Observed from Baseline Baseline [3] n 11 3 Mean (SD) 9.27 (2.810) 8.73 (0.577) Median 9.10 8.40 Min, Max 4.7, 15.8 8.4, 9.4 95% CI [4] (7.38, 11.16) (7.30, 10.17) sUA <6 1 ( 9.1%) 0 mg/dL, n (%) Day 1-Post- Infusion n 8 8 8 3 3 3 Mean (SD) 8.38 (2.042) 0.83 (0.798) −7.55 (2.158) 8.73 (0.577) 2.13 (2.438) −6.60 (2.848) Median 8.30 0.30 −7.50 8.40 1.20 −7.20 Min, Max 4.7, 11.4 0.3, 2.4 −11.1, −4.4 8.4, 9.4 0.3, 4.9 −9.1, −3.5 95% CI [4] (6.67, 10.08) (0.16, 1.49) (−9.35, −5.75) (7.30, 10.17) (0.00, 8.19) (−13.67, 0.47) sUA <6 8 (100%) 3 (100%) mg/dL, n (%) Week 1 n 4 4 4 2 2 2 Mean (SD) 7.18 (1.836) 0.30 (0.000) −6.88 (1.836) 8.40 (0.000) 0.30 (0.000) −8.10 (0.000) Median 7.45 0.30 −7.15 8.40 0.30 −8.10 Min, Max 4.7, 9.1 0.3, 0.3 −8.8, −4.4 8.4, 8.4 0.3, 0.3 −8.1, −8.1 95% CI [4] (4.25, 10.10) (0.30, 0.30) (−9.80, −3.95) (8.40, 8.40) (0.30, 0.30) (−8.10, −8.10) sUA <6 4 (100%) 2 (100%) mg/dL, n (%) Week 2-Pre- Infusion n 11 11 11 3 3 3 Mean (SD) 9.27 (2.810) 0.63 (1.096) −8.64 (2.086) 8.73 (0.577) 3.57 (3.775) −5.17 (4.225) Median 9.10 0.30 −8.80 8.40 2.70 −5.70 Min, Max 4.7, 15.8 0.3, 3.9 −11.9, −4.4 8.4, 9.4 0.3, 7.7 −9.1, −0.7 95% CI [4] (7.38, 11.16) (0.00, 1.37) (−10.04, −7.24) (7.30, 10.17) (0.00, 12.95) (−15.66, 5.33) sUA <6 11 (100%) 2 (66.7%) mg/dL, n (%) Week 2-Post- Infusion n 11 11 11 3 3 3 Mean (SD) 9.27 (2.810) 0.30 (0.000) −8.97 (2.810) 8.73 (0.577) 0.30 (0.000) −8.43 (0.577) Median 9.10 0.30 −8.80 8.40 0.30 −8.10 Min, Max 4.7, 15.8 0.3, 0.3 −15.5, −4.4 8.4, 9.4 0.3, 0.3 −9.1, −8.1 95% CI [4] (7.38, 11.16) (0.30, 0.30) (−10.86, −7.08) (7.30, 10.17) (0.30, 0.30) (−9.87, −7.00) sUA <6 11 (100%) 3 (100%) mg/dL, n (%) Week 4-Pre- Infusion n 11 11 11 3 3 3 Mean (SD) 9.27 (2.810) 0.68 (1.043) −8.59 (2.884) 8.73 (0.577) 5.03 (4.177) −3.70 (4.744) Median 9.10 0.30 −8.60 8.40 6.60 −1.80 Min, Max 4.7, 15.8 0.3, 3.8 −15.5, −4.4 8.4, 9.4 0.3, 8.2 −9.1, −0.2 95% CI [4] (7.38, 11.16) (0.00, 1.38) (−10.53, −6.65) (7.30, 10.17) (0.00, 15.41) (−15.49, 8.09) sUA <6 11 (100%) 1 ( 33.3%) mg/dL, n (%) Week 4-Post- Infusion n 11 11 11 2 2 2 Mean (SD) 9.27 (2.810) 0.30 (0.000) −8.97 (2.810) 8.90 (0.707) 0.30 (0.000) −8.60 (0.707) Median 9.10 0.30 −8.80 8.90 0.30 −8.60 Min, Max 4.7, 15.8 0.3, 0.3 −15.5, −4.4 8.4, 9.4 0.3, 0.3 −9.1, −8.1 95% CI [4] (7.38, 11.16) (0.30, 0.30) (−10.86, −7.08) (2.55, 15.25) (0.30, 0.30) (−14.95, −2.25) sUA <6 11 (100%) 2 (100%) mg/dL, n (%) Week 6-Pre- Infusion n 11 11 11 2 2 2 Mean (SD) 9.27 (2.810) 0.30 (0.000) −8.97 (2.810) 8.90 (0.707) 4.25 (5.586) −4.65 (6.293) Median 9.10 0.30 −8.80 8.90 4.25 −4.65 Min, Max 4.7, 15.8 0.3, 0.3 −15.5, −4.4 8.4, 9.4 0.3, 8.2 −9.1, −0.2 95% CI [4] (7.38, 11.16) (0.30, 0.30) (−10.86, −7.08) (2.55, 15.25) (0.00, 54.44) (−61.19, 51.89) sUA <6 11 (100%) 1 ( 50.0%) mg/dL, n (%) Week 6-Post- Infusion n 11 11 11 1 1 1 Mean (SD) 9.27 (2.810) 0.30 (0.000) −8.97 (2.810) 9.40 (NE) 0.30 (NE) −9.10 (NE) Median 9.10 0.30 −8.80 9.40 0.30 −9.10 Min, Max 4.7, 15.8 0.3, 0.3 −15.5, −4.4 9.4, 9.4 0.3, 0.3 −9.1, −9.1 95% CI [4] (7.38, 11.16) (0.30, 0.30) (−10.86, −7.08) (NE, NE) (NE, NE) (NE, NE) sUA <6 11 (100%) 1 (100%) mg/dL, n (%) Week 7 n 4 4 4 0 0 0 Mean (SD) 9.20 (4.755) 0.30 (0.000) −8.90 (4.755) Median 8.15 0.30 −7.85 Min, Max 4.7, 15.8 0.3, 0.3 −15.5, −4.4 95% CI [4] (1.63, 16.77) (0.30, 0.30) (−16.47, −1.33) sUA <6 4 (100%) 0 mg/dL, n (%) Week 8-Pre- Infusion n 11 11 11 1 1 1 Mean (SD) 9.27 (2.810) 0.37 (0.224) −8.91 (2.824) 9.40 (NE) 8.90 (NE) −0.50 (NE) Median 9.10 0.30 −8.60 9.40 8.90 −0.50 Min, Max 4.7, 15.8 0.3, 1.0 −15.5, −4.4 9.4, 9.4 8.9, 8.9 −0.5, −0.5 95% CI [4] (7.38, 11.16) (0.22, 0.52) (−10.80, −7.01) (NE, NE) (NE, NE) (NE, NE) sUA <6 11 (100%) 0 mg/dL, n (%) Week 8-Post- Infusion n 11 11 11 1 1 1 Mean (SD) 9.27 (2.810) 0.30 (0.000) −8.97 (2.810) 9.40 (NE) 0.30 (NE) −9.10 (NE) Median 9.10 0.30 −8.80 9.40 0.30 −9.10 Min, Max 4.7, 15.8 0.3, 0.3 −15.5, −4.4 9.4, 9.4 0.3, 0.3 −9.1, −9.1 95% CI [4] (7.38, 11.16) (0.30, 0.30) (−10.86, −7.08) (NE, NE) (NE, NE) (NE, NE) sUA <6 11 (100%) 1 (100%) mg/dL, n (%) Week 10-Pre- Infusion n 11 11 11 1 1 1 Mean (SD) 9.27 (2.810) 0.30 (0.000) −8.97 (2.810) 9.40 (NE) 8.10 (NE) −1.30 (NE) Median 9.10 0.30 −8.80 9.40 8.10 −1.30 Min, Max 4.7, 15.8 0.3, 0.3 −15.5, −4.4 9.4, 9.4 8.1, 8.1 −1.3, −1.3 95% CI [4] (7.38, 11.16) (0.30, 0.30) (−10.86, −7.08) (NE, NE) (NE, NE) (NE, NE) sUA <6 11 (100%) 0 mg/dL, n (%) Week 10-Post- Infusion n 11 11 11 0 0 0 Mean (SD) 9.27 (2.810) 0.30 (0.000) −8.97 (2.810) Median 9.10 0.30 −8.80 Min, Max 4.7, 15.8 0.3, 0.3 −15.5, −4.4 95% CI [4] (7.38, 11.16) (0.30, 0.30) (−10.86, −7.08) sUA <6 11 (100%) 0 mg/dL, n (%) Week 12-Pre- Infusion n 11 11 11 0 0 0 Mean (SD) 9.27 (2.810) 0.30 (0.015) −8.98 (2.806) Median 9.10 0.30 −8.80 Min, Max 4.7, 15.8 0.3, 0.3 −15.5, −4.4 95% CI [4] (7.38, 11.16) (0.29, 0.31) (−10.86, −7.09) sUA <6 11 (100%) 0 mg/dL, n (%) Week 12-Post- Infusion n 10 10 10 0 0 0 Mean (SD) 9.43 (2.911) 0.30 (0.000) −9.13 (2.911) Median 9.35 0.30 −9.05 Min, Max 4.7, 15.8 0.3, 0.3 −15.5, −4.4 95% CI [4] (7.35, 11.51) (0.30, 0.30) (−11.21, −7.05) sUA <6 10 (100%) 0 mg/dL, n (%) Week 14-Pre- Infusion n 11 11 11 0 0 0 Mean (SD) 9.27 (2.810) 0.30 (0.000) −8.97 (2.810) Median 9.10 0.30 −8.80 Min, Max 4.7, 15.8 0.3, 0.3 −15.5, −4.4 95% CI [4] (7.38, 11.16) (0.30, 0.30) (−10.86, −7.08) sUA <6 11 (100%) 0 mg/dL, n (%) Week 14-Post- Infusion n 10 10 10 0 0 0 Mean (SD) 9.31 (2.959) 0.30 (0.000) −9.01 (2.959) Median 9.35 0.30 −9.05 Min, Max 4.7, 15.8 0.3, 0.3 −15.5, −4.4 95% CI [4] (7.19, 11.43) (0.30, 0.30) (−11.13, −6.89) sUA <6 10 (100%) 0 mg/dL, n (%) Week 16-Pre- Infusion n 11 11 11 0 0 0 Mean (SD) 9.27 (2.810) 0.30 (0.000) −8.97 (2.810) Median 9.10 0.30 −8.80 Min, Max 4.7, 15.8 0.3, 0.3 −15.5, −4.4 95% CI [4] (7.38, 11.16) (0.30, 0.30) (−10.86, −7.08) sUA <6 11 (100%) 0 mg/dL, n (%) Week 16-Post- Infusion n 11 11 11 0 0 0 Mean (SD) 9.27 (2.810) 0.30 (0.000) −8.97 (2.810) Median 9.10 0.30 −8.80 Min, Max 4.7, 15.8 0.3, 0.3 −15.5, −4.4 95% CI [4] (7.38, 11.16) (0.30, 0.30) (−10.86, −7.08) sUA <6 11 (100%) 0 mg/dL, n (%) Week 18-Pre- Infusion n 11 11 11 0 0 0 Mean (SD) 9.27 (2.810) 0.30 (0.000) −8.97 (2.810) Median 9.10 0.30 −8.80 Min, Max 4.7, 15.8 0.3, 0.3 −15.5, −4.4 95% CI [4] (7.38, 11.16) (0.30, 0.30) (−10.86, −7.08) sUA <6 11 (100%) 0 mg/dL, n (%) Week 18-Post- Infusion n 11 11 11 0 0 0 Mean (SD) 9.27 (2.810) 0.30 (0.000) −8.97 (2.810) Median 9.10 0.30 −8.80 Min, Max 4.7, 15.8 0.3, 0.3 −15.5, −4.4 95% CI [4] (7.38, 11.16) (0.30, 0.30) (−10.86, −7.08) sUA <6 11 (100%) 0 mg/dL, n (%) Week 20-Pre- Infusion n 11 11 11 0 0 0 Mean (SD) 9.27 (2.810) 0.30 (0.000) −8.97 (2.810) Median 9.10 0.30 −8.80 Min, Max 4.7, 15.8 0.3, 0.3 −15.5, −4.4 95% CI [4] (7.38, 11.16) (0.30, 0.30) (−10.86, −7.08) sUA <6 11 (100%) 0 mg/dL, n (%) Week 20-Post- Infusion n 11 11 11 0 0 0 Mean (SD) 9.27 (2.810) 0.30 (0.000) −8.97 (2.810) Median 9.10 0.30 −8.80 Min, Max 4.7, 15.8 0.3, 0.3 −15.5, −4.4 95% CI [4] (7.38, 11.16) (0.30, 0.30) (−10.86, −7.08) sUA <6 11 (100%) 0 mg/dL, n (%) Week 22-Pre- Infusion n 11 11 11 0 0 0 Mean (SD) 9.27 (2.810) 0.30 (0.000) −8.97 (2.810) Median 9.10 0.30 −8.80 Min, Max 4.7, 15.8 0.3, 0.3 −15.5, −4.4 95% CI [4] (7.38, 11.16) (0.30, 0.30) (−10.86, −7.08) sUA <6 11(100%) 0 mg/dL, n (%) Week 22-Post- Infusion n 11 11 11 0 0 0 Median 9.10 0.30 −8.80 Min, Max 4.7, 15.8 0.3, 0.3 −15.5, −4.4 95% CI [4] (7.38, 11.16) (0.30, 0.30) (−10.86, −7.08) sUA <6 11 (100%) 0 mg/dL, n (%) Week 24-Pre- Infusion n 11 11 11 0 0 0 Mean (SD) 9.27 (2.810) 0.30 (0.000) −8.97 (2.810) Median 9.10 0.30 −8.80 Min, Max 4.7, 15.8 0.3, 0.3 −15.5, −4.4 95% CI [4] (7.38, 11.16) (0.30, 0.30) (−10.86, −7.08) sUA <6 11 (100%) 0 mg/dL, n (%) Week 24-Post- Infusion n 5 5 5 0 0 0 Mean (SD) 9.48 (4.135) 0.30 (0.000) −9.18 (4.135) Median 9.60 0.30 −9.30 Min, Max 4.7, 15.8 0.3, 0.3 −15.5, −4.4 95% CI [4] (4.35, 14.61) (0.30, 0.30) (−14.31, −4.05) sUA <6 5 (100%) 0 mg/dL, n (%) Week 26-Pre- Infusion n 8 8 8 0 0 0 Mean (SD) 9.41 (3.293) 0.30 (0.000) −9.11 (3.293) Median 9.25 0.30 −8.95 Min, Max 4.7, 15.8 0.3, 0.3 −15.5, −4.4 95% CI [4] (6.66, 12.17) (0.30, 0.30) (−11.87, −6.36) sUA <6 8 (100%) 0 mg/dL, n (%) Week 28-Pre- Infusion n 8 8 8 0 0 0 Mean (SD) 9.41 (3.293) 0.30 (0.000) −9.11 (3.293) Median 9.25 0.30 −8.95 Min, Max 4.7, 15.8 0.3, 0.3 −15.5, −4.4 95% CI [4] (6.66, 12.17) (0.30, 0.30) (−11.87, −6.36) sUA <6 8 (100%) 0 mg/dL, n (%) Week 30-Pre- Infusion n 8 8 8 0 0 0 Mean (SD) 9.41 (3.293) 0.30 (0.000) −9.11 (3.293) Median 9.25 0.30 −8.95 Min, Max 4.7, 15.8 0.3, 0.3 −15.5, −4.4 95% CI [4] (6.66, 12.17) (0.30, 0.30) (−11.87, −6.36) sUA <6 8 (100%) 0 mg/dL, n (%) Week 32-Pre- Infusion n 10 10 10 0 0 0 Mean (SD) 9.29 (2.961) 0.30 (0.000) −8.99 (2.961) Median 9.25 0.30 −8.95 Min, Max 4.7, 15.8 0.3, 0.3 −15.5, −4.4 95% CI [4] (7.17, 11.41) (0.30, 0.30) (−11.11, −6.87) sUA <6 10 (100%) 0 mg/dL, n (%) Week 32-Post- Infusion n 8 8 8 0 0 0 Mean (SD) 9.41 (3.293) 0.30 (0.000) −9.11 (3.293) Median 9.25 0.30 −8.95 Min, Max 4.7, 15.8 0.3, 0.3 −15.5, −4.4 95% CI [4] (6.66, 12.17) (0.30, 0.30) (−11.87, −6.36) sUA <6 8 (100%) 0 mg/dL, n (%) Week 34-Pre- Infusion n 10 10 10 0 0 0 Mean (SD) 9.29 (2.961) 0.82 (1.046) −8.47 (3.248) Median 9.25 0.30 −7.95 Min, Max 4.7, 15.8 0.3, 2.9 −15.5, −4.4 95% CI [4] (7.17, 11.41) (0.07, 1.57) (−10.79, −6.15) sUA <6 10 (100%) 0 mg/dL, n (%) Week 34-Post- Infusion n 8 8 8 0 0 0 Mean (SD) 9.41 (3.293) 0.30 (0.000) −9.11 (3.293) Median 9.25 0.30 −8.95 Min, Max 4.7, 15.8 0.3, 0.3 −15.5, −4.4 95% CI [4] (6.66, 12.17) (0.30, 0.30) (−11.87, −6.36) sUA <6 8 (100%) 0 mg/dL, n (%) Week 36-Pre- Infusion n 9 9 9 0 0 0 Mean (SD) 9.48 (3.077) 1.58 (2.425) −7.90 (4.094) Median 9.60 0.30 −8.60 Min, Max 4.7, 15.8 0.1, 6.4 −15.5, −2.5 95% CI [4] (7.11, 11.84) (0.00, 3.44) (−11.05, −4.75) sUA <6 8 ( 88.9%) 0 mg/dL, n (%) Week 36-Post- Infusion n 6 6 6 0 0 0 Mean (SD) 9.68 (3.799) 0.30 (0.000) −9.38 (3.799) Median 9.50 0.30 −9.20 Min, Max 4.7, 15.8 0.3, 0.3 −15.5, −4.4 95% CI [4] (5.70, 13.67) (0.30, 0.30) (−13.37, −5.40) sUA <6 6 (100%) 0 mg/dL, n (%) Week 38-Pre- Infusion n 5 5 5 0 0 0 Mean (SD) 9.34 (4.142) 0.93 (1.583) −8.41 (5.229) Median 8.90 0.30 −8.60 Min, Max 4.7, 15.8 0.0, 3.8 −15.5, −0.9 95% CI [4] (4.20, 14.48) (0.00, 2.90) (−14.90, −1.92) sUA <6 5 (100%) 0 mg/dL, n (%) Week 40-Pre- Infusion n 3 3 3 0 0 0 Mean (SD) 11.60 (3.686) 0.30 (0.000) −11.30 (3.686) Median 10.10 0.30 −9.80 Min, Max 8.9, 15.8 0.3, 0.3 −15.5, −8.6 95% CI [4] (2.44, 20.76) (0.30, 0.30) (−20.46, −2.14) sUA <6 3 (100%) 0 mg/dL, n (%) Week 42-Pre- Infusion n 3 3 3 0 0 0 Mean (SD) 11.60 (3.686) 0.30 (0.000) −11.30 (3.686) Median 10.10 0.30 −9.80 Min, Max 8.9, 15.8 0.3, 0.3 −15.5, −8.6 95% CI [4] (2.44, 20.76) (0.30, 0.30) (−20.46, −2.14) sUA <6 3 (100%) 0 mg/dL, n (%) Week 44-Pre- Infusion n 3 3 3 0 0 0 Mean (SD) 11.60 (3.686) 1.05 (1.305) −10.55 (4.625) Median 10.10 0.30 −9.80 Min, Max 8.9, 15.8 0.3, 2.6 −15.5, −6.3 95% CI [4] (2.44, 20.76) (0.00, 4.29) (−22.04, 0.94) sUA <6 3 (100%) 0 mg/dL, n (%) Week 46-Pre- Infusion n 2 2 2 0 0 0 Mean (SD) 12.95 (4.031) 0.30 (0.000) −12.65 (4.031) Median 12.95 0.30 −12.65 Min, Max 10.1, 15.8 0.3, 0.3 −15.5, −9.8 95% CI [4] (0.00, 49.16) (0.30, 0.30) (−48.86, 23.56) sUA <6 2 (100%) 0 mg/dL, n (%) Week 48-Pre- Infusion n 2 2 2 0 0 0 Mean (SD) 12.95 (4.031) 0.30 (0.000) −12.65 (4.031) Median 12.95 0.30 −12.65 Min, Max 10.1, 15.8 0.3, 0.3 −15.5, −9.8 95% CI [4] (0.00, 49.16) (0.30, 0.30) (−48.86, 23.56) sUA <6 2 (100%) 0 mg/dL, n (%) Week 48-Post- Infusion n 3 3 3 0 0 0 Mean (SD) 11.93 (3.350) 1.60 (2.252) −10.33 (4.922) Median 10.10 0.30 −9.80 Min, Max 9.9, 15.8 0.3, 4.2 −15.5, −5.7 95% CI [4] (3.61, 20.26) (0.00, 7.19) (−22.56, 1.89) sUA <6 3 (100%) 0 mg/dL, n (%) Week 50-Pre- Infusion n 2 2 2 0 0 0 Mean (SD) 12.95 (4.031) 0.30 (0.000) −12.65 (4.031) Median 12.95 0.30 −12.65 Min, Max 10.1, 15.8 0.3, 0.3 −15.5, −9.8 95% CI [4] (0.00, 49.16) (0.30, 0.30) (−48.86, 23.56) sUA <6 2 (100%) 0 mg/dL, n (%) Week 50-Post- Infusion n 3 3 3 0 0 0 Mean (SD) 11.93 (3.350) 1.37 (1.848) −10.57 (4.598) Median 10.10 0.30 −9.80 Min, Max 9.9, 15.8 0.3, 3.5 −15.5, −6.4 95% CI [4] (3.61, 20.26) (0.00, 5.96) (−21.99, 0.86) sUA <6 3 (100%) 0 mg/dL, n (%) Week 52/ET n 2 2 2 0 0 0 Mean (SD) 12.95 (4.031) 0.30 (0.000) −12.65 (4.031) Median 12.95 0.30 −12.65 Min, Max 10.1, 15.8 0.3, 0.3 −15.5, −9.8 95% CI [4] (0.00, 49.16) (0.30, 0.30) (−48.86, 23.56) sUA <6 2 (100%) 0 mg/dL, n (%) End of Pegloticase Infusions Visit n 2 2 2 0 0 0 Mean (SD) 8.80 (1.556) 0.30 (0.000) −8.50 (1.556) Median 8.80 0.30 −8.50 Min, Max 7.7, 9.9 0.3, 0.3 −9.6, −7.4 95% CI [4] (0.00, 22.78) (0.30, 0.30) (−22.48, 5.48) sUA <6 2 (100%) 0 mg/dL, n (%) Early Termination Visit n 0 0 0 3 3 3 Mean (SD) 8.73 (0.577) 8.17 (0.058) −0.57 (0.635) Median 8.40 8.20 −0.20 Min, Max 8.4, 9.4 8.1, 8.2 −1.3, −0.2 95% CI [4] (7.30, 10.17) (8.02, 8.31) (−2.14, 1.01) sUA <6 0 0 mg/dL, n (%)

TABLE 8 Serum Uric Acid < 6 mg/dL Responders during Month 9 and Month 12 (ITT Population and mITT Population) ITT Population mITT Population Time Point N = 15 N = 14 Month 9 (Weeks 32, 34, 36) Responder, n (%) [3] 10 (71.4) 10 (76.9) 95% Clopper-Pearson Confidence Interval [4] 41.9, 91.6  46.2, 95.0  Non-Responder, n (%) 4 (28.6) 3 (23.1) Number of subjects eligible for analysis [1] 14  13  Proportion of Time during Period that sUA < 6 mg/dL n 10  10  Mean (SD) 99.48 (1.656) 99.48 (1.656) Median  100.00  100.00 Min, Max 94.8, 100.0 94.8, 100.0 Month 9 (Weeks 32, 34, 36) Discontinued treatment due to stopping rule prior to Week 36, n (%)[2] 3 (21.4) 3 (23.1) Subjects missing all data in analysis period, n (%) 4 (28.6) 3 (23.1) Subjects with only one measurement (above cutoff) in analysis period, n (%) 0 0 Subjects with only one measurement (below cutoff) in analysis period, n (%) 0 0 Month 12 (Weeks 48, 50, 52) Responder, n (%) [5] 3 (21.4) 3 (23.1) 95% Clopper-Pearson Confidence Interval [4] 4.7, 50.8 5.0, 53.8 Non-Responder. n (%) 11 (78.6) 10   (76.9) Month 12 (Weeks 48, 50, 52) Number of subjects eligible for analysis [1] 14  13  Proportion of Time during Period that sUA < 6 mg/dL n 3 3 Mean (SD) 100.00 (0.000) 100.00 (0.000) Median  100.00  100.00 Min, Max 100.0, 100.0  100.0, 100.0  Month 12 (Weeks 48, 50, 52) Discontinued treatment due to stopping rule prior to Week 52, n (%)[2] 3 (21.4) 3 (23.1) Subjects missing all data in analysis period, n (%) 11 (78.6) 10 (76.9) Subjects with only one measurement (above cutoff) in analysis period, n (%) 0 0 Subjects with only one measurement (below cutoff) in analysis period, n (%) 0 0

TABLE 9 Serum Uric Acid < 5 mg/dL Responders during Month 9 and Month 12 (ITT Population and mITT Population) ITT Population mITT Population Time Point N = 15 N = 14 Month 9 (Weeks 32, 34, 36) Responder, n (%) [3] 10 (71.4) 10   (76.9) 95% Clopper-Pearson Confidence Interval [4] 41.9, 91.6 46.2, 95.0  Non-Responder, n (%) 4 (28.6) 3 (23.1) Number of subjects eligible for analysis 111 14  13  Proportion of Time during Period that sUA < 5 mg/dL n 10  10  Mean (SD) 97.73 (5.805) 97.73 (5.805) Median  100.00  100.00 Min, Max  81.7, 100.0 81.7, 100.0 Month 9 (Weeks 32. 34. 36) Discontinued treatment due to stopping rule prior to Week 36, n (%)[2] 3 (21.4) 3 (23.1) Subjects missing all data in analysis period, n (%) 4 (28.6) 3 (23.1) Subjects with only one measurement (above cutoff) in analysis period, n (%) 0 0 Subjects with only one measurement (below cutoff) in analysis period, n (%) 0 0 Month 12 (Weeks 48, 50, 52) Responder, n (%) [5] 3 (21.4) 3 (23.1) 95% Clopper-Pearson Confidence Interval [4]  4.7, 50.8 5.0, 53.8 Non-Responder, n (%) 11 (78.6) 10 (76.9) Month 12 (Weeks 48, 50, 52) Number of subjects eligible for analysis [1] 14  13  Proportion of Time during Period that sUA < 5 mg/dL n 3 3 Mean (SD) 100.00 (0.000) 100.00 (0.000) Median 100.00 100.00 Min, Max 100.0, 100.0 100.0, 100.0  Month 12 (Weeks 48, 50, 52) Discontinued treatment due to stopping rule prior to Week 52, n (%)[2] 3 (21.4) 3 (23.1) Subjects missing all data in analysis period, n (%) 11 (78.6) 10 (76.9) Subjects with only one measurement (above cutoff) in analysis period, n (%) 0 0 Subjects with only one measurement (below cutoff) in analysis period, n (%) 0 0

TABLE 10 Time to First Pre-infusion Serum Uric Acid > 6 mg/dU and Time to 2 Consecutive Pre-infusion Serum Uric Acid > 6 mg/dU (mITT Population) mITT Population N = 14 Had pre-Infusion sUA > 6 mg/dL post-Day 1 Pegloticase Infusion, n (%) Yes 4 (28.6) No 10 (71.4) Time to pre-infusion sUA > 6 mg/dL post-Day 1 Pegloticase Infusion (days) [1] Mean (SD) 218.3 (110.41) Min, Max  16, 353 Kaplan-Meier Estimate Median NE 95% CI 57.0, NE Had 2 Consecutive Pre-Infusion sUA > 6 mg/dL post- Day 1 Pegloticase Infusion, n (%) Yes 3 (21.4) No 11 (78.6) Time to 2 Consecutive Pre-Infusion sUA > 6 mg/dL post-Day 1 Pegloticase Infusion (days) [2] Mean (SD) 218.3 (110.41) Min, Max  16, 353 Kaplan-Meier Estimate Median NE 95% CI 57.0, NE

TABLE 11 Assessment of Number of Joints Affected by Tophi (mITT Population) mITT Population (N = 14) Change from Visit Statistics Baseline [1] Observed Baseline Screening n 13  Mean (SD) 6.9 (7.94) Median   4.0 Min, Max 1, 31 Week 24 n 9 9 9 Mean (SD) 8.7 (9.10) 4.0 (3.64)  −4.7 (6.36) Median   7.0   3.0  −3.0 Min, Max 1, 31  1, 12 −19, 2  Week 36 n 4 4 4 Mean (SD) 14.8 (11.15) 3.3 (3.86) −11.5 (7.33) Median  10.5   1.5  −9.0 Min, Max 7, 31 1, 9 −22, −6  Week 52/ET n 2 2 2 Mean (SD) 22.0 (12.73) 5.0 (2.83) −17.0 (9.90) Median  22.0   5.0 −17.0  Min, Max 13, 31  3, 7 −24, −10

TABLE 12 Tender Joint Count and Swollen Joint Count: Observed Values and Change from Methotrexate Baseline Values (mITT Population) mITT Population (N = 14) Visit Change from Parameter Statistics Baseline [1] Observed Baseline Tender Baseline [2] Joint Count n 14   Mean (SD) 11.6 (15.06) Median 7.5 Min, Max 0, 51 Day 1 n 14   14   14   Mean (SD) 11.6 (15.06)  9.6 (11.03) −1.9 (9.75) Median 7.5 7.0 0.0 Min, Max 0, 51 0, 37 −23, 11 95% CI [3] −7.6, 3.7 Week 14 n 14   14   14   Mean (SD) 11.6 (15.06) 4.6 (6.16)  −7.0 (14.20) Median 7.5 2.0 0.0 Min, Max 0, 51 0, 18 −43, 5  95% CI [3] −15.2, 1.2  Tender Week 24 Joint Count n 11   11   11   Mean (SD) 12.8 (16.68) 2.6 (3.88) −10.2 (14.27) Median 7.0 0.0 −4.0  Min, Max 0, 51 0, 11 −40, 0  95% CI [3] −19.8, −0.6 Week 36 n 9   9   9   Mean (SD) 14.4 (18.12) 2.1 (4.54) −12.3 (14.56) Median 7.0 0.0 −7.0  Min, Max 0, 51 0, 14 −37, 0  95% CI [3] −23.5, −1.1 Week 52/ET n 3   3   3   Mean (SD) 29.3 (18.93) 5.3 (3.21) −24.0 (21.38) Median 21.0  4.0 −17.0  Min, Max 16, 51  3, 9  −48, −7 95% CI [3] −77.1, 29.1 Tender End of Joint Count Pegloticase Infusions Visit n 2   2   2   Mean (SD) 14.0 (9.90)  2.0 (2.83) −12.0 (7.07)   Median 14.0  2.0 −12.0  Min, Max 7, 21 0, 4  −17, −7 95% CI [3] −75.5, 51.5 Early Termination Visit n 3   3   3   Mean (SD) 7.0 (6.56) 7.7 (8.96)  0.7 (5.13) Median 8.0 3.0 2.0 Min, Max 0, 13 2, 18 −5, 5 95% CI [3] −12.1, 13.4 Swollen Baseline [2] Joint Count n 14   Mean (SD) 6.0 (9.25) Median 2.0 Min, Max 0, 28 Swollen Day 1 Joint Count n 14   14   14   Mean (SD) 6.0 (9.25) 5.3 (6.94) −0.7 (5.21) Median 2.0 3.5 0.5 Min, Max 0, 28 0, 26 −12, 6  95% CI [3] −3.7, 2.3 Week 14 n 14   14   14   Mean (SD) 6.0 (9.25) 1.7 (3.73) −4.3 (7.38) Median 2.0 0.0 −2.0  Min, Max 0, 28 0, 13 −27, 0  95% CI [3] −8.5, 0.0 Week 24 n 11   11   11   Mean (SD)  7.2 (10.16) 0.5 (1.21) −6.6 (9.03) Median 3.0 0.0 −3.0  Min, Max 0, 28 0, 3  −25, 0  95% CI [3] −12.7, −0.6 Swollen Week 36 Joint Count n 9   9   9   Mean (SD)  7.9 (11.04) 0.1 (0.33)  −7.8 (10.81) Median 3.0 0.0 −3.0  Min, Max 0, 28 0, 1  −27, 0  95% CI [3] −16.1, 0.5  Week 52/ET n 3   3   3   Mean (SD) 21.0 (9.64)   0.0 (0.00) −21.0 (9.64)   Median 25.0  0.0 −25.0  Min, Max 10, 28  0, 0   −28, −10 95% CI [3] −45.0, 3.0  End of Pegloticase Infusions Visit n 2   2   2   Mean (SD) 7.0 (4.24) 0.0 (0.00) −7.0 (4.24) Median 7.0 0.0 −7.0  Min, Max 4, 10 0, 0  −10, −4 95% CI [3] −45.1, 31.1 Swollen Early Joint Count Termination Visit n 3   3   3   Mean (SD) 1.7 (2.08) 0.7 (0.58) −1.0 (1.73) Median 1.0 1.0 0.0 Min, Max 0, 4  0, 1  −3, 0 95% CI [3] −5.3, 3.3

TABLE 13 Tender Joint Count and Swollen Joint Count: Observed Values and Change from Pegloticase Baseline Values (mITT Population) mITT Population (N = 14) Visit Change from Parameter Statistics Baseline [1] Observed Baseline Tender Baseline [2] Joint Count n 14   Mean (SD)  9.6 (11.03) Median 7.0 Min, Max  0, 37 Week 14 n 14   14   14   Mean (SD)  9.6 (11.03) 4.6 (6.16) −5.1 (8.12) Median 7.0 2.0 −5.0 Min, Max 0, 37  0, 18 −29, 6  95% CI [3]  −9.8, −0.4 Week 24 n 11   11   11   Mean (SD)  9.5 (11.29) 2.6 (3.88) −6.8 (8.16) Median 7.0 0.0 −4.0 Min, Max 0, 37  0, 11 −26, 1  95% CI [3] −12.3, −1.3 Tender Week 36 Joint Count n 9   9   9  Mean (SD)  9.9 (12.57) 2.1 (4.54) −7.8 (8.94) Median 4.0 0.0 −4.0 Min, Max 0, 37  0, 14 −23, 0  95% CI [3] −14.7, −0.9 Week 52/ET n 3   3   3  Mean (SD) 21.3 (17.16) 5.3 (3.21) −16.0 (17.52) Median 24.0  4.0 −15.0  Min, Max 3, 37 3, 9 −34, 1  95% CI [3] −59.5, 27.5 End of Pegloticase Infusions Visit n 2   2   2  Mean (SD) 5.0 (2.83) 2.0 (2.83) −3.0 (5.66) Median 5.0 2.0 −3.0 Min, Max 3, 7  0, 4 −7, 1 95% CI [3] −53.8, 47.8 Tender Early Joint Count Termination Visit n 3   3   3  Mean (SD) 10.3 (12.34) 7.7 (8.96) −2.7 (4.16) Median 7.0 3.0 −4.0 Min, Max 0, 24  2, 18 −6, 2 95% CI [3] −13.0, 7.7  Swollen Baseline [2] Joint Count n 14   Mean (SD) 5.3 (6.94) Median 3.5 Min, Max  0, 26 Week 14 n 14   14   14   Mean (SD) 5.3 (6.94) 1.7 (3.73) −3.6 (7.04) Median 3.5 0.0 −2.5 Min, Max 0, 26  0, 13 −25, 7  95% CI [3] −7.6, 0.5 Swollen Week 24 Joint Count n 11   11   11   Mean (SD) 5.6 (7.71) 0.5 (1.21) −5.1 (6.66) Median 3.0 0.0 −3.0 Min, Max 0, 26 0, 3 −23, 0  95% CI [3]  −9.6, −0.6 Week 36 n 9   9   9  Mean (SD) 6.3 (8.44) 0.1 (0.33) −6.2 (8.15) Median 4.0 0.0 −4.0 Min, Max 0, 26 0, 1 −25, 0  95% CI [3] −12.5, 0.0  Week 52/ET n 3   3   3  Mean (SD) 13.0 (13.00) 0.0 (0.00) −13.0 (13.00) Median 13.0  0.0 −13.0  Min, Max 0, 26 0, 0 −26, 0  95% CI [3] −45.3, 19.3 Swollen End of Joint Count Pegloticase Infusions Visit n 2   2   2  Mean (SD) 2.0 (2.83) 0.0 (0.00) −2.0 (2.83) Median 2.0 0.0 −2.0 Min, Max 0, 4  0, 0 −4, 0 95% CI [3] −27.4, 23.4 Early Termination Visit n 3   3   3  Mean (SD) 4.0 (3.61) 0.7 (0.58) −3.3 (3.06) Median 5.0 1.0 −4.0 Min, Max 0, 7  0, 1 −6, 0 95% CI [3] −10.9, 4.3 

TABLE 14 Health Assessment Questionnaire: Observed Values and Change from Methotrexate Baseline Values (mITT Population) mITT Population (N = 14) Visit Change from Parameter Statistics Baseline [1] Observed Baseline HAQ-DI Baseline [2] n 14   Mean (SD) 0.7 (0.71) Median  0.6 Min, Max 0, 2 Day 1 n 13   13   13  Mean (SD) 0.8 (0.71) 0.8 (0.77)  0.1 (0.27) Median  0.6  0.5   0.0 Min, Max 0, 2 0, 2 −0, 1 95% CI [3] −0.1, 0.2 Week 14 n 14   14   14  Mean (SD) 0.7 (0.71) 0.5 (0.41) −0.2 (0.77) Median  0.6  0.5   0.0 Min, Max 0, 2 0, 1 −2, 1 95% CI [3] −0.7, 0.2 HAQ-DI Week 24 n 11   11   11  Mean (SD) 0.8 (0.77) 0.2 (0.33) −0.5 (0.74) Median  0.6  0.1  −0.1 Min, Max 0, 2 0, 1 −2, 0 95% CI [3] −1.0, 0.0 Week 36 n 9  9  9 Mean (SD) 0.8 (0.86) 0.3 (0.49) −0.5 (0.80) Median  0.4  0.1   0.0 Min, Max 0, 2 0, 1 −2, 0 95% CI [3] −1.1, 0.1 Week 52/ET n 3  3  3 Mean (SD) 1.0 (0.76) 0.4 (0.29) −0.6 (0.87) Median  0.9  0.3  −0.1 Min, Max 0, 2 0, 1  −2, −0 95% CI [3] −2.8, 1.5 HAQ-DI End of Pegloticase Infusions Visit n 2  2  2 Mean (SD) 0.3 (0.18) 0.1 (0.18) −0.1 (0.35) Median  0.3  0.1  −0.1 Min, Max 0, 0 0, 0 −0, 0 95% CI [3] −3.3, 3.1 Early Termination Visit n 3  3  3 Mean (SD) 0.5 (0.45) 0.7 (0.51)  0.2 (0.90) Median  0.6  0.6  −0.3 Min, Max 0, 1 0, 1 −0, 1 95% CI [3] −2.0, 2.5 HAQ-Pain Baseline [2] n 14   Mean (SD) 40.9 (23.30) Median 47.5 Min, Max  0, 75 HAQ-Pain Day 1 n 13   13   13  Mean (SD) 40.2 (24.10) 42.5 (22.24)  2.3 (19.93) Median 45.0 40.0   0.0 Min, Max  0, 75  3, 80 −27, 47 95% CI [3]  −9.7, 14.4 Week 14 n 14   14   14  Mean (SD) 40.9 (23.30) 27.1 (26.25) −13.9 (30.48) Median 47.5 15.0 −12.5  Min, Max  0, 75  0, 90 −60, 60 95% CI [3] −31.5, 3.7  Week 24 n 11   11   11  Mean (SD) 44.5 (22.96) 25.4 (27.50) −19.2 (35.13) Median 50.0 20.0 −10.0  Min, Max  0, 75  0, 80 −75, 55 95% CI [3] −42.8, 4.4  HAQ-Pain Week 36 n 9  9  9 Mean (SD) 43.9 (23.02) 21.0 (27.60) −22.9 (28.41) Median 50.0 10.0 −20.0  Min, Max  0, 75  0, 80 −74, 30 95% CI [3] −44.7, −1.1 Week 52/ET n 3  3  3 Mean (SD) 46.7 (22.55) 4.0 (5.20) −42.7 (18.04) Median 45.0  1.0 −44.0  Min, Max 25, 70  1, 10 −60, −24 95% CI [3] −87.5, 2.1  End of Pegloticase Infusions Visit n 2  2  2 Mean (SD) 37.5 (17.68) 40.0 (56.57)  2.5 (74.25) Median 37.5 40.0   2.5 Min, Max 25, 50  0, 80 −50, 55 95% CI [3] −664.6, 669.6 HAQ-Pain Early Termination Visit n 3  3  3 Mean (SD) 27.7 (23.59) 46.7 (40.41)  19.0 (36.51) Median 30.0 40.0   7.0 Min, Max  3, 50 10, 90 −10, 60 95% CI [3]  −71.7, 109.7 HAQ-Health Baseline [2] n 14   Mean (SD) 49.1 (30.79) Median 55.0 Min, Max  0, 90 Day 1 n 13   13   13  Mean (SD) 46.7 (30.68) 37.8 (27.06)  −8.8 (38.29) Median 50.0 25.0  10.0 Min, Max  0, 90  2, 75 −70, 55 95% CI [3] −32.0, 14.3 HAQ-Health Week 14 n 14   14   14  Mean (SD) 49.1 (30.79) 36.6 (33.87) −12.5 (36.79) Median 55.0 16.5  −5.0 Min, Max  0, 90  0, 90 −75, 60 95% CI [3] −33.7, 8.7  Week 24 n 11   11   11  Mean (SD) 54.5 (29.02) 21.4 (26.65) −33.2 (36.01) Median 60.0 10.0 −40.0  Min, Max  0, 90  0, 80 −80, 20 95% CI [3] −57.4, −9.0 Week 36 n 9  9  9 Mean (SD) 55.0 (30.41) 27.3 (35.18) −27.7 (42.59) Median 60.0 10.0 −10.0  Min, Max  0, 90  0, 100 −85, 20 95% CI [3] −60.4, 5.1  HAQ-Health Week 52/ET n 3  3  3 Mean (SD) 76.7 (15.28) 60.0 (48.22) −16.7 (59.23) Median 80.0 80.0  15.0 Min, Max 60, 90  5, 95 −85, 20 95% CI [3] −163.8, 130.5 End of Pegloticase Infusions Visit n 2  2  2 Mean (SD) 80.0 (0.00)  0.0 (0.00) −80.0 (0.00)  Median 80.0  0.0 −80.0  Min, Max 80, 80 0, 0  −80, −80 95% CI [3]  −80.0, −80.0 Early Termination Visit n 3   3  3 Mean (SD) 29.0 (34.39) 28.3 (40.72)  −0.7 (16.77) Median 20.0 10.0   8.0 Min, Max  0, 67  0, 75 −20, 10 95% CI [3] −42.3, 41.0

TABLE 15 Health Assessment Questionnaire: Observed Values and Change from Pegloticase Baseline Values (mITT Population) mITT Population (N = 14) Visit Change from Parameter Statistics Baseline [1] Observed Baseline HAQ-DI Baseline [2] n 14   Mean (SD) 0.8 (0.76) Median 0.5 Min, Max 0, 2 Week 14 n 14   14   14  Mean (SD) 0.8 (0.76) 0.5 (0.41) −0.3 (0.80) Median  0.5 0.5   0.0 Min, Max 0, 2 0, 1 −2, 1 95% CI [3] −0.7, 0.2 Week 24 n 11   11   11  Mean (SD) 0.8 (0.86) 0.2 (0.33) −0.6 (0.85) Median  0.4 0.1  −0.1 Min, Max 0, 2 0, 1 −2, 0 95% CI [3] −1.2, 0.0 HAQ-DI Week 36 n 9  9   9 Mean (SD) 0.9 (0.93) 0.3 (0.49) −0.5 (0.86) Median  0.4 0.1  −0.1 Min, Max 0, 2 0, 1 −2, 0 95% CI [3] −1.2, 0.1 Week 52/ET n 3  3   3 Mean (SD) 1.2 (0.97) 0.4 (0.29) −0.8 (1.08) Median  0.9 0.3  −0.1 Min, Max 0, 2 0, 1  −2, −0 95% CI [3] −3.4, 1.9 End of Pegloticase Infusions Visit n 2  2   2 Mean (SD) 0.3 (0.18) 0.1 (0.18) −0.1 (0.35) Median  0.3 0.1  −0.1 Min, Max 0, 0 0, 0 −0, 0 95% CI [3] −3.3, 3.1 HAQ-DI Early Termination Visit n 3  3   3 Mean (SD) 0.5 (0.07) 0.7 (0.51)  0.2 (0.56) Median  0.5 0.6   0.1 Min, Max 1, 1 0, 1 −0, 1 95% CI [3] −1.2, 1.6 HAQ-Pain Baseline [2] n 14   Mean (SD) 43.1 (21.46) Median 45.0  Min, Max  3, 80 Week 14 n 14   14   14  Mean (SD) 43.1 (21.46) 27.1 (26.25) −16.0 (30.65) Median 45.0 15.0  −12.5  Min, Max  3, 80  0, 90 −65, 50 95% CI [3] −33.7, 1.7  HAQ-Pain Week 24 n 11   11   11  Mean (SD) 42.1 (24.23) 25.4 (27.50) −16.7 (38.53) Median 30.0 20.0  −10.0  Min, Max  3, 80  0, 80 −66, 55 95% CI [3] −42.6, 9.2  Week 36 n 9  9   9 Mean (SD) 40.9 (25.46) 21.0 (27.60) −19.9 (20.25) Median 30.0 10.0  −20.0  Min, Max  3, 80  0, 80 −59, 10 95% CI [3] −35.5, −4.3 Week 52/ET n 3  3   3 Mean (SD) 45.0 (30.41) 4.0 (5.20) −41.0 (25.24) Median 30.0 1.0 −29.0  Min, Max 25, 80  1, 10  −70, −24 95% CI [3] −103.7, 21.7  HAQ-Pain End of Pegloticase Infusions Visit n 2  2   2 Mean (SD) 37.5 (17.68) 40.0 (56.57)  2.5 (74.25) Median 37.5 40.0    2.5 Min, Max 25, 50  0, 80 −50, 55 95% CI [3] −664.6, 669.6 Early Termination Visit n 3  3   3 Mean (SD) 46.7 (5.77) 46.7 (40.41)  0.0 (45.83) Median 50.0 40.0  −10.0  Min, Max 40, 50 10, 90 −40, 50 95% CI [3] −113.8, 113.8 HAQ-Health Baseline [2] n 14   Mean (SD) 40.9 (28.33) Median 32.5  Min, Max  2, 80 HAQ-Health Week 14 n 14   14   14  Mean (SD) 40.9 (28.33) 36.6 (33.87)  −4.3 (43.82) Median 32.5 16.5   −1.0 Min, Max  2, 80  0, 90 −75, 75 95% CI [3] −29.6, 21.0 Week 24 n 11   11   11  Mean (SD) 41.1 (29.29) 21.4 (26.65) −19.7 (43.38) Median 40.0 10.0  −10.0  Min, Max  2, 80  0, 80 −80, 55 95% CI [3] −48.9, 9.4  Week 36 n 9  9   9 Mean (SD) 43.6 (31.78) 27.3 (35.18) −16.2 (50.72) Median 50.0 10.0  −10.0  Min, Max  2, 80  0, 100 −80, 90 95% CI [3] −55.2, 22.8 HAQ-Health Week 52/ET n 3  3   3 Mean (SD) 36.7 (34.03) 60.0 (48.22)  23.3 (54.85) Median 25.0 80.0    5.0 Min, Max 10, 75  5, 95 −20, 85 95% CI [3] −112.9, 159.6 End of Pegloticase Infusions Visit n 2  2   2 Mean (SD) 45.0 (49.50) 0.0 (0.00) −45.0 (49.50) Median 45.0 0.0 −45.0  Min, Max 10, 80 0, 0  −80, −10 95% CI [3] −489.7, 399.7 Early Termination Visit n 3  3   3 Mean (SD) 40.0 (30.41) 28.3 (40.72) −11.7 (62.52) Median 25.0 10.0  −10.0  Min, Max 20, 75  0, 75 −75, 50 95% CI [3] −167.0, 143.6

TABLE 16 Patient Global Assessment of Gout and Physician Global Assessment of Gout: Observed Values and Change from Methotrexate Baseline Values (mITT Population) mITT Population (N = 14) Visit Change from Parameter Statistics Baseline [1] Observed Baseline Patient Baseline [2] Global n 14   Assessment Mean (SD) 5.6 (2.21) of Gout Median 6.0 Min, Max  1, 10 Day 1 n 14   14   14   Mean (SD) 5.6 (2.21) 5.8 (1.76)  0.2 (1.85) Median 6.0 6.0  0.0 Min, Max  1, 10 3, 8 −3, 4  95% CI [3] −0.9, 1.3  Week 14 n 14   14   14   Mean (SD) 5.6 (2.21) 3.1 (2.27) −2.5 (2.77) Median 6.0 3.0 −2.5 Min, Max  1, 10 0, 9 −6, 4  95% CI [3] −4.1, −0.9 Patient Week 24 Global n 11   11   11   Assessment Mean (SD) 5.7 (2.45) 2.0 (1.79) −3.7 (3.23) of Gout Median 6.0 3.0 −3.0 Min, Max  1, 10 0, 4 −10, 0  95% CI [3] −5.9, −1.6 Week 36 n 9   9   9  Mean (SD) 5.6 (2.07) 2.1 (2.80) −3.4 (2.92) Median 6.0 1.0 −4.0 Min, Max 1, 8 0, 8 −8, 2  95% CI [3] −5.7, −1.2 Week 52/ET n 3   3   3  Mean (SD) 5.3 (1.53) 1.0 (1.00) −4.3 (0.58) Median 5.0 1.0 −4.0 Min, Max 4, 7 0, 2 −5, −4 95% CI [3] −5.8, −2.9 Patient End of Global Pegloticase Assessment Infusions of Gout Visit n 2   2   2  Mean (SD) 6.0 (1.41) 2.0 (2.83) −4.0 (4.24) Median 6.0 2.0 −4.0 Min, Max 5, 7 0, 4 −7, −1 95% CI [3] −42.1, 34.1  Early Termination Visit n 3   3   3  Mean (SD) 5.0 (1.00) 5.7 (3.06)  0.7 (2.89) Median 5.0 5.0 −1.0 Min, Max 4, 6 3, 9 −1, 4  95% CI [3] −6.5, 7.8  Physician Baseline [2] Global n 14   Assessment Mean (SD) 6.1 (2.25) of Gout Median 7.0 Min, Max 1, 9 Physician Day 1 Global n 14   14   14   Assessment Mean (SD) 6.1 (2.25) 6.0 (2.45) −0.1 (2.35) of Gout Median 7.0 7.0  0.0 Min, Max 1, 9 0, 9 −6, 4  95% CI [3] −1.5, 1.2  Week 14 n 14   14   14   Mean (SD) 6.1 (2.25) 1.9 (1.64) −4.2 (2.22) Median 7.0 2.0 −5.0 Min, Max 1, 9 0, 6 −8, −1 95% CI [3] −5.5, −2.9 Week 24 n 11   11   11   Mean (SD) 6.1 (2.39) 0.8 (0.87) −5.3 (2.10) Median 7.0 1.0 −6.0 Min, Max 1, 9 0, 3 −8, −1 95% CI [3] −6.7, −3.9 Physician Week 36 Global n 9   9   9  Assessment Mean (SD) 6.6 (2.40) 0.7 (1.00) −5.9 (2.03) of Gout Median 7.0 0.0 −6.0 Min, Max 1, 9 0, 2 −8, −1 95% CI [3] −7.4, −4.3 Week 52/ET n 3   3   3  Mean (SD) 8.3 (0.58) 1.0 (0.00) −7.3 (0.58) Median 8.0 1.0 −7.0 Min, Max 8, 9 1, 1 −8, −7 95% CI [3] −8.8, −5.9 End of Pegloticase Infusions Visit n 2   2   2  Mean (SD) 7.5 (0.71) 0.5 (0.71) −7.0 (0.00) Median 7.5 0.5 −7.0 Min, Max 7, 8 0, 1 −7, −7 95% CI [3] −7.0, −7.0 Physician Early Global Termination Assessment Visit of Gout n 3   3   3  Mean (SD) 6.3 (2.08) 3.7 (2.08) −2.7 (2.08) Median 7.0 3.0 −2.0 Min, Max 4, 8 2, 6 −5, −1 95% CI [3] −7.8, 2.5 

TABLE 17 Patient Global Assessment of Gout and Physician Global Assessment of Gout: Observed Values and Change from Pegloticase Baseline Values (mITT Population) mITT Population (N = 14) Parameter Visit Statistics Baseline [1] Observed Change from Baseline Patient Global Assessment of Gout Baseline [2] n 14 Mean (SD) 5.8 (1.76) Median 6.0 Min, Max 3, 8 Week 14 n 14 14 14 Mean (SD) 5.8 (1.76) 3.1 (2.27) −2.7 (2.43) Median 6.0 3.0 −3.0 Min, Max 3, 8 0, 9 −6, 4  95% CI [3] −4.1, −1.3 Week 24 n 11 11 11 Mean (SD) 5.9 (1.97) 2.0 (1.79) −3.9 (2.51) Median 7.0 3.0 −4.0 Min, Max 3, 8 0, 4 −8, 0  95% CI [3] −5.6, −2.2 Patient Global Assessment of Gout Week 36 n 9 9 9 Mean (SD) 5.6 (2.01) 2.1 (2.80) −3.4 (2.46) Median 6.0 1.0 −3.0 Min, Max 3, 8 0, 8 −7, 0  95% CI [3] −5.3, −1.6 Week 52/ET n 3 3 3 Mean (SD) 5.3 (2.08) 1.0 (1.00) −4.3 (1.15) Median 6.0 1.0 −5.0 Min, Max 3, 7 0, 2 −5, −3 95% CI [3] −7.2, −1.5 End of Pegloticase Infusions Visit n 2 2 2 Mean (SD) 6.5 (0.71) 2.0 (2.83) −4.5 (3.54) Median 6.5 2.0 −4.5 Min, Max 6, 7 0, 4 −7, −2 95% CI [3] −36.3, 27.3  Patient Global Assessment of Gout Early Termination Visit n 3 3 3 Mean (SD) 5.3 (0.58) 5.7 (3.06)  0.3 (3.51) Median 5.0 5.0 0.0 Min, Max 5, 6 3, 9 −3, 4  95% CI [3] −8.4, 9.1  Physician Global Assessment of Gout Baseline [2] n 14 Mean (SD) 6.0 (2.45) Median 7.0 Min, Max 0, 9 Week 14 n 14 14 14 Mean (SD) 6.0 (2.45) 1.9 (1.64) −4.1 (2.40) Median 7.0 2.0 −4.5 Min, Max 0, 9 0, 6 −8, 0  95% CI [3] −5.5, −2.7 Physician Global Assessment of Gout Week 24 n 11 11 11 Mean (SD) 6.1 (2.70) 0.8 (0.87) −5.3 (2.41) Median 7.0 1.0 −6.0 Min, Max 0, 9 0, 3 −8, 0  95% CI [3] −6.9, −3.7 Week 36 n 9 9 9 Mean (SD) 6.1 (2.98) 0.7 (1.00) −5.4 (2.46) Median 7.0 0.0 −7.0 Min, Max 0, 9 0, 2 −7, 0  95% CI [3] −7.3, −3.6 Week 52/ET n 3 3 3 Mean (SD) 8.3 (1.15) 1.0 (0.00) −7.3 (1.15) Median 9.0 1.0 −8.0 Min, Max 7, 9 1, 1 −8, −6 95% CI [3] −10.2, −4.5  Physician Global Assessment of Gout End of Pegloticase Infusions Visit n 2 2 2 Mean (SD) 7.0 (0.00) 0.5 (0.71) −6.5 (0.71) Median 7.0 0.5 −6.5 Min, Max 7, 7 0, 1 −7, −6 95% CI [3] −12.9, −0.1  Early Termination Visit n 3 3 3 Mean (SD) 5.7 (1.53) 3.7 (2.08) −2.0 (1.00) Median 6.0 3.0 −2.0 Min, Max 4, 7 2, 6 −3, −1 95% CI [3] −4.5, 0.5 

Joint Pain Assessment after Treatment with KXX and MTX

TABLE 18 Joint Pain Associated with Gout Assessment: Observed Values and Change from Methotrexate Baseline Values (mITT Population) mITT Population (N = 14) Parameter Visit Statistics Baseline [1] Observed Change from Baseline Average Joint Pain Baseline [2] n 14 Mean (SD) 4.9 (2.18) Median 5.0 Min, Max 0, 8 Day 1 n 14 14 14 Mean (SD) 4.9 (2.18) 4.9 (1.94)  0.1 (1.54) Median 5.0 5.5 0.0 Min, Max 0, 8 2, 8 −3, 3 95% CI [3] −0.8, 1.0 Week 14 n 14 14 14 Mean (SD) 4.9 (2.18) 3.2 (2.42) −1.6 (3.00) Median 5.0 2.5 −1.5 Min, Max 0, 8 0, 9 −6, 6 95% CI [3] −3.4, 0.1 Average Joint Pain Week 24 n 11 11 11 Mean (SD) 5.1 (2.39) 2.3 (2.41) −2.8 (3.28) Median 6.0 2.0 −3.0 Min, Max 0, 8 0, 8 −8, 3 95% CI [3]  −5.0, −0.6 Week 36 n 9 9 9 Mean (SD) 5.1 (2.62) 2.1 (2.76) −3.0 (2.78) Median 6.0 1.0 −2.0 Min, Max 0, 8 0, 8 −8, 1 95% CI [3]  −5.1, −0.9 Week 52/ET n 3 3 3 Mean (SD) 5.0 (2.00) 2.0 (0.00) −3.0 (2.00) Median 5.0 2.0 −3.0 Min, Max 3, 7 2, 2  −5, −1 95% CI [3] −8.0, 2.0 Average Joint Pain End of Pegloticase Infusions Visit n 2 2 2 Mean (SD) 6.0 (1.41) 4.0 (5.66) −2.0 (7.07) Median 6.0 4.0 −2.0 Min, Max 5, 7 0, 8 −7, 3 95% CI [3] −65.5, 61.5 Early Termination Visit n 3 3 3 Mean (SD) 4.0 (1.00) 6.0 (3.00)  2.0 (3.61) Median 4.0 6.0 1.0 Min, Max 3, 5 3, 9 −1, 6 95% CI [3]  −7.0, 11.0 Least Joint Pain Baseline [2] n 14 Mean (SD) 3.1 (2.03) Median 3.5 Min, Max 0, 6 Least Joint Pain Day 1 n 14 14 14 Mean (SD) 3.1 (2.03) 3.4 (2.47)  0.3 (1.73) Median 3.5 3.0 0.5 Min, Max 0, 6 0, 8 −4, 3 95% CI [3] −0.7, 1.3 Week 14 n 14 14 14 Mean (SD) 3.1 (2.03) 1.7 (1.20) −1.4 (2.14) Median 3.5 2.0 −1.5 Min, Max 0, 6 0, 3 −6, 3 95% CI [3]  −2.7, −0.2 Week 24 n 11 11 11 Mean (SD) 3.5 (2.02) 1.1 (1.45) −2.4 (1.86) Median 4.0 0.0 −2.0 Min, Max 0, 6 0, 4 −5, 0 95% CI [3]  −3.6, −1.1 Least Joint Pain Week 36 n 9 9 9 Mean (SD) 3.2 (2.17) 1.3 (2.69) −1.9 (2.15) Median 3.0 0.0 −2.0 Min, Max 0, 6 0, 8 −5, 2 95% CI [3]  −3.5, −0.2 Week 52/ET n 3 3 3 Mean (SD) 3.7 (2.08) 1.0 (1.00) −2.7 (1.15) Median 3.0 1.0 −2.0 Min, Max 2, 6 0, 2  −4, −2 95% CI [3] −5.5, 0.2 End of Pegloticase Infusions Visit n 2 2 2 Mean (SD) 4.0 (1.41) 0.0 (0.00) −4.0 (1.41) Median 4.0 0.0 −4.0 Min, Max 3, 5 0, 0  −5, −3 95% CI [3] −16.7, 8.7  Least Joint Pain Early Termination Visit n 3 3 3 Mean (SD) 2.0 (2.00) 3.0 (0.00)  1.0 (2.00) Median 2.0 3.0 1.0 Min, Max 0, 4 3, 3 −1, 3 95% CI [3] −4.0, 6.0 Worst Joint Pain Baseline [2] n 14 Mean (SD) 5.8 (2.49) Median 6.0 Min, Max 0, 9 Day 1 n 14 14 14 Mean (SD) 5.8 (2.49) 6.3 (2.23)  0.5 (2.28) Median 6.0 7.0 0.5 Min, Max 0, 9 2, 9 −3, 4 95% CI [3] −0.8, 1.8 Worst Joint Pain Week 14 n 14 14 14 Mean (SD) 5.8 (2.49) 4.4 (2.76) −1.4 (3.16) Median 6.0 3.5 −1.0 Min, Max 0, 9 0, 9 −6, 6 95% CI [3] −3.3, 0.4 Week 24 n 11 11 11 Mean (SD) 5.9 (2.66) 2.9 (2.66) −3.0 (4.22) Median 6.0 3.0 −2.0 Min, Max 0, 9 0, 8 −9, 5 95% CI [3]  −5.8, −0.2 Week 36 n 9 9 9 Mean (SD) 5.7 (2.74) 2.8 (3.15) −2.9 (3.44) Median 6.0 2.0 −3.0 Min, Max 0, 9 0, 8 −9, 2  95% CI [3]  −5.5, −0.2 Worst Joint Pain Week 52/ET n 3 3 3 Mean (SD) 5.0 (2.00) 2.0 (1.00) −3.0 (1.73) Median 5.0 2.0 −2.0 Min, Max 3, 7 1, 3  −5, −2 95% CI [3] −7.3, 1.3 End of Pegloticase Infusions Visit n 2 2 2 Mean (SD) 5.5 (3.54) 4.0 (5.66) −1.5 (9.19) Median 5.5 4.0 −1.5 Min, Max 3, 8 0, 8 −8, 5 95% CI [3] −84.1, 81.1 Early Termination Visit n 3 3 3 Mean (SD) 5.3 (2.08) 7.3 (1.53)  2.0 (3.46) Median 6.0 7.0 0.0 Min, Max 3, 7 6, 9  0, 6 95% CI [3]  −6.6, 10.6

Chronic Response to Treatment with KXX+MTX

TABLE 19 Gout Chronic Response - Relative to Methotrexate Baseline (mITT Population) Visit in Dual Parameter mITT Population Therapy Period Category Statistics N = 14 Day 1 GCR20 20% Reduction in Tender Joint Count, n/m (%) 6/13 (46.2) 20% Reduction in Swollen Joint Count, n/m (%) 4/13 (30.8) 20% Reduction in HAQ-Health Score, n/m (%) 5/12 (41.7) 20% Reduction in HAQ-Pain, n/m (%) 4/12 (33.3) GCR20 Responders [1], n (%) 2/13 (15.4) 95% Confidence Interval [2] 1.9, 45.4 GCR50 50% Reduction in Tender Joint Count, n/m (%) 4/13 (30.8) 50% Reduction in Swollen Joint Count, n/m (%) 3/13 (23.1) 50% Reduction in HAQ-Health Score, n/m (%) 5/12 (41.7) 50% Reduction in HAQ-Pain, n/m (%) 1/12 (8.3) GCR50 Responders [1], n (%) 1/13 (7.7) 95% Confidence Interval [2] 0.2, 36.0 GCR70 70% Reduction in Tender Joint Count, n/m (%) 3/13 (23.1) 70% Reduction in Swollen Joint Count, n/m (%) 3/13 (23.1) 70% Reduction in HAQ-Health Score, n/m (%) 4/12 (33.3) 70% Reduction in HAQ-Pain, n/m (%) 1/12 (8.3) GCR70 Responders [1], n (%) 1/13 (7.7) 95% Confidence Interval [2] 0.2, 36.0 Week 14 GCR20 20% Reduction in Tender Joint Count, n/m (%) 9/13 (69.2) 20% Reduction in Swollen Joint Count, n/m (%) 12/13 (92.3) 20% Reduction in HAQ-Health Score, n/m (%) 7/13 (53.8) 20% Reduction in HAQ-Pain, n/m (%) 9/13 (69.2) GCR20 Responders [1], n (%) 8/13 (61.5) 95% Confidence Interval [2] 31.6, 86.1  GCR50 50% Reduction in Tender Joint Count, n/m (%) 9/13 (69.2) 50% Reduction in Swollen Joint Count, n/m (%) 10/13 (76.9) 50% Reduction in HAQ-Health Score, n/m (%) 6/13 (46.2) 50% Reduction in HAQ-Pain, n/m (%) 7/13 (53.8) GCR50 Responders [1], n (%) 6/13 (46.2) 95% Confidence Interval [2] 19.2, 74.9  GCR70 70% Reduction in Tender Joint Count, n/m (%) 7/13 (53.8) 70% Reduction in Swollen Joint Count, n/m (%) 10/13 (76.9) 70% Reduction in HAQ-Health Score, n/m (%) 5/13 (38.5) 70% Reduction in HAQ-Pain, n/m (%) 5/13 (38.5) GCR70 Responders [1], n (%) 5/13 (38.5) 95% Confidence Interval [2] 13.9, 68.4  Week 24 GCR20 20% Reduction in Tender Joint Count, n/m (%) 10/10 (100) 20% Reduction in Swollen Joint Count, n/m (%) 10/10 (100) 20% Reduction in HAQ-Health Score, n/m (%) 7/10 (70.0) 20% Reduction in HAQ-Pain, n/m (%) 9/10 (90.0) GCR20 Responders [1], n (%) 10/10 (100) 95% Confidence Interval [2] 69.2, 100.0 GCR50 50% Reduction in Tender Joint Count, n/m (%) 9/10 (90.0) 50% Reduction in Swollen Joint Count, n/m (%) 10/10 (100) 50% Reduction in HAQ-Health Score, n/m (%) 7/10 (70.0) 50% Reduction in HAQ-Pain, n/m (%) 5/10 (50.0) GCR50 Responders [1], n (%) 6/10 (60.0) 95% Confidence Interval [2] 26.2, 87.8  GCR70 70% Reduction in Tender Joint Count, n/m (%) 8/10 (80.0) 70% Reduction in Swollen Joint Count, n/m (%) 10/10 (100) 70% Reduction in HAQ-Health Score, n/m (%) 6/10 (60.0) 70% Reduction in HAQ-Pain, n/m (%) 5/10 (50.0) GCR70 Responders [1], n (%) 6/10 (60.0) 95% Confidence Interval [2] 26.2, 87.8  Week 36 GCR20 20% Reduction in Tender Joint Count, n/m (%) 9/9 (100) 20% Reduction in Swollen Joint Count, n/m (%) 9/9 (100) 20% Reduction in HAQ-Health Score, n/m (%) 6/9 (66.7) 20% Reduction in HAQ-Pain, n/m (%) 8/9 (88.9) GCR20 Responders [1], n (%) 8/9 (88.9) 95% Confidence Interval [2] 51.8, 99.7  GCR50 50% Reduction in Tender Joint Count, n/m (%) 9/9 (100) 50% Reduction in Swollen Joint Count, n/m (%) 9/ 9 (100) 50% Reduction in HAQ-Health Score, n/m (%) 6/9 (66.7) 50% Reduction in HAQ-Pain, n/m (%) 6/9 (66.7) GCR50 Responders [1], n (%) 8/9 (88.9) 95% Confidence Interval [2] 51.8, 99.7  GCR70 70% Reduction in Tender Joint Count, n/m (%) 9/ 9 (100) 70% Reduction in Swollen Joint Count, n/m (%) 9/9 (100) 70% Reduction in HAQ-Health Score, n/m (%) 4/ 9 (44.4) 70% Reduction in HAQ-Pain, n/m (%) 5/9 (55.6) GCR70 Responders [1], n (%) 6/9 (66.7) 95% Confidence Interval [2] 29.9, 92.5  Week 52/ET GCR20 20% Reduction in Tender Joint Count, n/m (%) 3/3 (100) 20% Reduction in Swollen Joint Count, n/m (%) 3/3 (100) 20% Reduction in HAQ-Health Score, n/m (%) 1/3 (33.3) 20% Reduction in HAQ-Pain, n/m (%) 3/3 (100) GCR20 Responders [1], n (%) 3/3 (100) 95% Confidence Interval [2] 29.2, 100.0 GCR50 50% Reduction in Tender Joint Count, n/m (%) 2/3 (66.7) 50% Reduction in Swollen Joint Count, n/m (%) 3/3 (100) 50% Reduction in HAQ-Health Score, n/m (%) 1/3 (33.3) 50% Reduction in HAQ-Pain, n/m (%) 3/3 (100) GCR50 Responders [1], n (%) 3/3 (100) 95% Confidence Interval [2] 29.2, 100.0 GCR70 70% Reduction in Tender Joint Count, n/m (%) 2/3 (66.7) 70% Reduction in Swollen Joint Count, n/m (%) 3/3 (100) 70% Reduction in HAQ-Health Score, n/m (%) 1/3 (33.3) 70% Reduction in HAQ-Pain, n/m (%) 3/3 (100) GCR70 Responders [1], n (%) 3/3 (100) 95% Confidence Interval [2] 29.2, 100.0

TABLE 20 Gout Chronic Response - Relative to Pegloticase Baseline (mITT Population) Visit in Dual Parameter mITT Population Therapy Period Category Statistics N = 14 Week 14 GCR20 20% Reduction in Tender Joint Count, n/m (%) 11/13 (84.6) 20% Reduction in Swollen Joint Count, n/m (%) 11/13 (84.6) 20% Reduction in HAQ-Health Score, n/m (%) 6/13 (46.2) 20% Reduction in HAQ-Pain, n/m (%) 9/13 (69.2) GCR20 Responders [1], n (%) 8/13 (61.5) 95% Confidence Interval [2] 31.6, 86.1 GCR50 50% Reduction in Tender Joint Count, n/m (%) 8/13 (61.5) 50% Reduction in Swollen Joint Count, n/m (%) 11/13 (84.6) 50% Reduction in HAQ-Health Score, n/m (%) 4/13 (30.8) 50% Reduction in HAQ-Pain, n/m (%) 7/13 (53.8) GCR50 Responders [1], n (%) 5/13 (38.5) 95% Confidence Interval [2] 13.9, 68.4 GCR70 70% Reduction in Tender Joint Count, n/m (%) 7/13 (53.8) 70% Reduction in Swollen Joint Count, n/m (%) 11/13 (84.6) 70% Reduction in HAQ-Health Score, n/m (%) 3/13 (23.1) 70% Reduction in HAQ-Pain, n/m (%) 5/13 (38.5) GCR70 Responders [1], n (%) 4/13 (30.8) 95% Confidence Interval [2]  9.1, 61.4 Week 24 GCR20 20% Reduction in Tender Joint Count, n/m (%) 9/10 (90.0) 20% Reduction in Swollen Joint Count, n/m (%) 10/10 (100) 20% Reduction in HAQ-Health Score, n/m (%) 6/10 (60.0) 20% Reduction in HAQ-Pain, n/m (%) 6/10 (60.0) GCR20 Responders [1], n (%) 6/10 (60.0) 95% Confidence Interval [2] 26.2, 87.8 GCR50 50% Reduction in Tender Joint Count, n/m (%) 8/10 (80.0) 50% Reduction in Swollen Joint Count, n/m (%) 10/10 (100) 50% Reduction in HAQ-Health Score, n/m (%) 6/10 (60.0) 50% Reduction in HAQ-Pain, n/m (%) 5/10 (50.0) GCR50 Responders [1], n (%) 5/10 (50.0) 95% Confidence Interval [2] 18.7, 81.3 GCR70 70% Reduction in Tender Joint Count, n/m (%) 7/10 (70.0) 70% Reduction in Swollen Joint Count, n/m (%) 10/10 (100) 70% Reduction in HAQ-Health Score, n/m (%) 6/10 (60.0) 70% Reduction in HAQ-Pain, n/m (%) 5/10 (50.0) GCR70 Responders [1], n (%) 5/10 (50.0) 95% Confidence Interval [2] 18.7, 81.3 Week 36 GCR20 20% Reduction in Tender Joint Count, n/m (%) 9/9 (100) 20% Reduction in Swollen Joint Count, n/m (%) 9/9 (100) 20% Reduction in HAQ-Health Score, n/m (%) 5/9 (55.6) 20% Reduction in HAQ-Pain, n/m (%) 7/9 (77.8) GCR20 Responders [1], n (%) 7/9 (77.8) 95% Confidence Interval [2] 40.0, 97.2 GCR50 50% Reduction in Tender Joint Count, n/m (%) 8/9 (88.9) 50% Reduction in Swollen Joint Count, n/m (%) 9/9 (100) 50% Reduction in HAQ-Health Score, n/m (%) 5/9 (55.6) 50% Reduction in HAQ-Pain, n/m (%) 5/9 (55.6) GCR50 Responders [1], n (%) 6/9 (66.7) 95% Confidence Interval [2] 29.9, 92.5 GCR70 70% Reduction in Tender Joint Count, n/m (%) 7/9 (77.8) 70% Reduction in Swollen Joint Count, n/m (%) 9/9 (100) 70% Reduction in HAQ-Health Score, n/m (%) 5/9 (55.6) 70% Reduction in HAQ-Pain, n/m (%) 4/9 (44.4) GCR70 Responders [1], n (%) 4/9 (44.4) 95% Confidence Interval [2] 13.7, 78.8 Week 52/ET GCR20 20% Reduction in Tender Joint Count, n/m (%) 2/3 (66.7) 20% Reduction in Swollen Joint Count, n/m (%) 3/3 (100) 20% Reduction in HAQ-Health Score, n/m (%) 1/3 (33.3) 20% Reduction in HAQ-Pain, n/m (%) 3/3 (100) GCR20 Responders [1], n (%) 2/3 (66.7) 95% Confidence Interval [2]  9.4, 99.2 GCR50 50% Reduction in Tender Joint Count, n/m (%) 2/3 (66.7) 50% Reduction in Swollen Joint Count, n/m (%) 3/3 (100) 50% Reduction in HAQ-Health Score, n/m (%) 1/3 (33.3) 50% Reduction in HAQ-Pain, n/m (%) 3/3 (100) GCR50 Responders [1], n (%) 2/3 (66.7) 95% Confidence Interval [2]  9.4, 99.2 GCR70 70% Reduction in Tender Joint Count, n/m (%) 1/3 (33.3) 70% Reduction in Swollen Joint Count, n/m (%) 3/3 (100) 70% Reduction in HAQ-Health Score, n/m (%) 1/3 (33.3) 70% Reduction in HAQ-Pain, n/m (%) 3/3 (100) GCR70 Responders [1], n (%) 2/3 (66.7) 95% Confidence Interval [2]  9.4, 99.2

Assessment of Safety of KXX+MTX Treatment (ADD 195-200 HERE (SAFETY))

TABLE 21 Treatment-Emergent Adverse Events by System Organ Class and Preferred Term during the Methotrexate Run-in Period (ITT Population and mITT Population) ITT Population (N = 15)/ mITT Population (N = 14)/ Total PY of MTX = 1.1 Total PY of MTX = 1.0 System Organ Class Total Events/Incidence Rate Total Events/Incidence Rate Preferred Term n (%) (Events/PY of MTX) n (%) (Events/PY of MTX) Any TEAEs 10 (66.7) 20/18.2 10 (71.4) 20/20.0 Blood And Lymphatic System Disorders 1 (6.7) 2/1.8 1 (7.1) 2/2.0 Leukopenia 1 (6.7) 1/0.9 1 (7.1) 1/1.0 Neutropenia 1 (6.7) 1/0.9 1 (7.1) 1/1.0 Eye Disorders 1 (6.7) 1/0.9 1 (7.1) 1/1.0 Dry Eye 1 (6.7) 1/0.9 1 (7.1) 1/1.0 Gastrointestinal Disorders 5 (33.3) 6/5.5 5 (35.7) 6/6.0 Abdominal Discomfort 2 (13.3) 2/1.8 2 (14.3) 2/2.0 Dental Caries 1 (6.7) 1/0.9 1 (7.1) 1/1.0 Diarrhoea 1 (6.7) 1/0.9 1 (7.1) 1/1.0 Nausea 2 (13.3) 2/1.8 2 (14.3) 2/2.0 Infections And Infestations 2 (13.3) 2/1.8 2 (14.3) 2/2.0 Chronic Sinusitis 1 (6.7) 1/0.9 1 (7.1) 1/1.0 Nasopharyngitis 1 (6.7) 1/0.9 1 (7.1) 1/1.0 Metabolism And Nutrition Disorders 5 (33.3) 6/5.5 5 (35.7) 6/6.0 Gout 5 (33.3) 6/5.5 5 (35.7) 6/6.0 Nervous System Disorders 1 (6.7) 1/0.9 1 (7.1) 1/1.0 Headache 1 (6.7) 1/0.9 1 (7.1) 1/1.0 Respiratory, Thoracic And Mediastinal Disorders 1 (6.7) 1/0.9 1 (7.1) 1/1.0 Cough 1 (6.7) 1/0.9 1 (7.1) 1/1.0 Skin And Subcutaneous Tissue Disorders 1 (6.7) 1/0.9 1 (7.1) 1/1.0 Pruritus 1 (6.7) 1/0.9 1 (7.1) 1/1.0

TABLE 22 Treatment-Emergent Adverse Events by System Organ Class and Preferred Term during the Pegloticase + Immunomodulator Period Through Week 24 (mITT Population) mITT Population (N = 14)/ Total PY of MTX = 5.2/ Total PY of Pegloticase = 5.4 System Organ Class Total Events/Incidence Rate Total Events/Incidence Rate Preferred Term n (%) (Events/PY of MTX) (Events/PY of Pegloticase) Any TEAEs 14 (100) 110/21.2  110/20.4  Eye Disorders 1 (7.1) 1/0.2 1/0.2 Eye Irritation 1 (7.1) 1/0.2 1/0.2 Gastrointestinal Disorders 4 (28.6) 7/1.3 7/1.3 Abdominal Pain 1 (7.1) 1/0.2 1/0.2 Constipation 1 (7.1) 1/0.2 1/0.2 Diarrhoea 3 (21.4) 3/0.6 3/0.6 Gastrooesophageal Reflux Disease 1 (7.1) 1/0.2 1/0.2 Tooth Impacted 1 (7.1) 1/0.2 1/0.2 General Disorders And Administration Site 1 (7.1) 1/0.2 1/0.2 Conditions Non-Cardiac Chest Pain 1 (7.1) 1/0.2 1/0.2 Hepatobiliary Disorders 1 (7.1) 1/0.2 1/0.2 Cholecystitis Acute 1 (7.1) 1/0.2 1/0.2 Infections And Infestations 7 (50.0) 10/1.9  10/1.9  Bacterial Sepsis 1 (7.1) 1/0.2 1/0.2 Chronic Sinusitis 1 (7.1) 1/0.2 1/0.2 Gastroenteritis Viral 1 (7.1) 1/0.2 1/0.2 Influenza 1 (7.1) 1/0.2 1/0.2 Nasopharyngitis 1 (7.1) 1/0.2 1/0.2 Sinusitis 2 (14.3) 2/0.4 2/0.4 Upper Respiratory Tract Infection 3 (21.4) 3/0.6 3/0.6 Injury, Poisoning And Procedural Complications 3 (21.4) 4/0.8 4/0.7 Infusion Related Reaction 1 (7.1) 1/0.2 1/0.2 Limb Injury 1 (7.1) 1/0.2 1/0.2 Muscle Strain 2 (14.3) 2/0.4 2/0.4 Investigations 2 (14.3) 2/0.4 2/0.4 Alanine Aminotransferase Increased 1 (7.1) 1/0.2 1/0.2 Liver Function Test Increased 1 (7.1) 1/0.2 1/0.2 Metabolism And Nutrition Disorders 12 (85.7) 68/13.1 68/12.6 Gout 12 (85.7) 67/12.9 67/12.4 Hypercholesterolaemia 1 (7.1) 1/0.2 1/0.2 Musculoskeletal And Connective Tissue Disorders 3 (21.4) 3/0.6 3/0.6 Arthralgia 1 (7.1) 1/0.2 1/0.2 Plantar Fasciitis 1 (7.1) 1/0.2 1/0.2 Tendonitis 1 (7.1) 1/0.2 1/0.2 Nervous System Disorders 3 (21.4) 4/0.8 4/0.7 Carpal Tunnel Syndrome 1 (7.1) 1/0.2 1/0.2 Dysgeusia 1 (7.1) 1/0.2 1/0.2 Headache 1 (7.1) 1/0.2 1/0.2 Parosmia 1 (7.1) 1/0.2 1/0.2 Renal And Urinary Disorders 1 (7.1) 1/0.2 1/0.2 Dysuria 1 (7.1) 1/0.2 1/0.2 Respiratory, Thoracic And Mediastinal Disorders 1 (7.1) 1/0.2 1/0.2 Cough 1 (7.1) 1/0.2 1/0.2 Skin And Subcutaneous Tissue Disorders 3 (21.4) 4/0.8 4/0.7 Pruritus 1 (7.1) 2/0.4 2/0.4 Rash Papular 1 (7.1) 1/0.2 1/0.2 Skin Lesion 1 (7.1) 1/0.2 1/0.2 Vascular Disorders 2 (14.3) 2/0.4 2/0.4 Hypertension 2 (14.3) 2/0.4 2/0.4 Uncoded 1 (7.1) 1/0.2 1/0.2 Uncoded 1 (7.1) 1/0.2 1/0.2

Assessment of Adverse Events for Treatment with KXX+MTX (ADD 230-248 HERE (GOUT FLARE))

TABLE 23 Treatment-Emergent Adverse Events of Special Interest during the Methotrexate Run-in Period: Gout Flares (ITT Population and mITT Population) ITT Population mITT Population Preferred Term N = 15 N = 14 Gout Flares, n (%) 5 (33.3) 5 (35.7) Number of Gout Flares per Subject, n (%) 1 4 (26.7) 4 (28.6) 2 1 (6.7) 1 (7.1) Among subjects with at least one gout flare Mean (SD) 1.2 (0.45) 1.2 (0.45) Median 1.0 1.0 Min, Max 1, 2 1, 2

TABLE 24 Treatment-Emergent Adverse Events of Special Interest during the Pegloticase + Immunomodulator Period Through Week 24: Gout Flares (mITT Population) mITT Population Preferred Term N = 14 Time Period n/m (%) Gout Flares Full Pegloticase + Immunomodulator Period 12/14 (85.7) Number of Gout Flares per Subject  1 1/14 (7.1)  2 2/14 (14.3)  3 1/14 (7.1)  4 1/14 (7.1)  5 3/14 (21.4)  6 1/14 (7.1)  9 1/14 (7.1) 10 1/14 (7.1) 15 1/14 (7.1) Among subjects with at least one gout flare Mean (SD) 5.6 (4.01) Median 5.0 Min, Max  1, 15 Day 1-Week 12 of the Pegloticase + 12/14 (85.7) Immunomodulator Period Number of Gout Flares per Subject  1 1/14 (7.1)  2 2/14 (14.3)  3 1/14 (7.1)  4 3/14 (21.4)  5 1/14 (7.1)  6 2/14 (14.3)  7 1/14 (7.1)  8 1/14 (7.1) Among subjects with at least one gout flare Mean (SD) 4.3 (2.15) Median 4.0 Min, Max 1, 8 >Week 12-Week 24 of the Pegloticase + 5/11 (45.5) Immunomodulator Period Number of Gout Flares per Subject  1 2/11 (18.2)  2 1/11 (9.1)  4 1/11 (9.1)  7 1/11 (9.1) Among subjects with at least one gout flare Mean (SD) 3.0 (2.55) Median 2.0 Min, Max 1, 7

TABLE 25 Assessment of Gout Flares during the Methotrexate Run-in Period and Pegloticase + Immunomodulator Period (ITT Population and mITT Population) ITT Population mITT Population Time Point N = 15 N = 14 Week −4 Number Assessed 14 13 Any Gout Flares Since the Last Visit, n (%) 8 (57.1) 7 (53.8) If Yes, the following are assessed Pain different than normal, n (%) 6 (42.9) 5 (38.5) Pain at rest > 3 out of 10, n (%) 7 (50.0) 6 (46.2) Swelling in Joints, n (%) 7 (50.0) 6 (46.2) Maximum Reported Intensity of Flare (0-10 scale) [1] n 6 5 Mean (SD) 8.5 (1.22) 8.2 (1.10) Median 8.0 8.0 Min, Max  7, 10  7, 10 Day 1 Number Assessed 14 14 Any Gout Flares Since the Last Visit, n (%) 8 (57.1) 8 (57.1) If Yes, the following are assessed Pain different than normal, n (%) 7 (50.0) 7 (50.0) Pain at rest > 3 out of 10, n (%) 8 (57.1) 8 (57.1) Swelling in Joints, n (%) 6 (42.9) 6 (42.9) Maximum Reported Intensity of Flare (0-10 scale) [1] n 8 8 Mean (SD) 5.8 (1.28) 5.8 (1.28) Median 5.5 5.5 Min, Max 4, 8 4, 8 Week 2 Number Assessed NA 14 Any Gout Flares Since the Last Visit, n (%) 12 (85.7) If Yes, the following are assessed Pain different than normal, n (%) 11 (78.6) Pain at rest > 3 out of 10, n (%) 12 (85.7) Swelling in Joints, n (%) 10 (71.4) Maximum Reported Intensity of Flare (0-10 scale) [1] n 12 Mean (SD) 6.5 (1.17) Median 7.0 Min, Max 4, 8 Week 4 Number Assessed NA 14 Any Gout Flares Since the Last Visit, n (%) 11 (78.6) If Yes, the following are assessed Pain different than normal, n (%) 9 (64.3) Pain at rest > 3 out of 10, n (%) 9 (64.3) Swelling in Joints, n (%) 9 (64.3) Maximum Reported Intensity of Flare (0-10 scale) [1] n 11 Mean (SD) 6.5 (2.62) Median 7.0 Min, Max  2, 10 Week 6 Number Assessed NA 13 Any Gout Flares Since the Last Visit, n (%) 9 (69.2) If Yes, the following are assessed Pain different than normal, n (%) 8 (61.5) Pain at rest > 3 out of 10, n (%) 7 (53.8) Swelling in Joints, n (%) 8 (61.5) Maximum Reported Intensity of Flare (0-10 scale) [1] n 9 Mean (SD) 6.0 (2.18) Median 6.0 Min, Max 3, 9 Week 8 Number Assessed NA 12 Any Gout Flares Since the Last Visit, n (%) 7 (58.3) If Yes, the following are assessed Pain different than normal, n (%) 5 (41.7) Pain at rest > 3 out of 10, n (%) 6 (50.0) Swelling in Joints, n (%) 5 (41.7) Maximum Reported Intensity of Flare (0-10 scale) [1] n 6 Mean (SD) 5.8 (2.23) Median 6.0 Min, Max 2, 8 Week 10 Number Assessed NA 12 Any Gout Flares Since the Last Visit, n (%) 6 (50.0) If Yes, the following are assessed Pain different than normal, n (%) 4 (33.3) Pain at rest > 3 out of 10, n (%) 4 (33.3) Swelling in Joints, n (%) 4 (33.3) Maximum Reported Intensity of Flare (0-10 scale) [1] n 5 Mean (SD) 6.2 (2.86) Median 6.0 Min, Max  3, 10 Week 12 Number Assessed NA 11 Any Gout Flares Since the Last Visit, n (%) 7 (63.6) If Yes, the following are assessed Pain different than normal, n (%) 5 (45.5) Pain at rest > 3 out of 10, n (%) 5 (45.5) Swelling in Joints, n (%) 4 (36.4) Maximum Reported Intensity of Flare (0-10 scale) [1] n 6 Mean (SD) 4.3 (0.82) Median 4.5 Min, Max 3, 5 Week 14 Number Assessed NA 11 Any Gout Flares Since the Last Visit, n (%) 5 (45.5) If Yes, the following are assessed Pain different than normal, n (%) 4 (36.4) Pain at rest > 3 out of 10, n (%) 3 (27.3) Swelling in Joints, n (%) 3 (27.3) Maximum Reported Intensity of Flare (0-10 scale) [1] n 4 Mean (SD) 5.0 (2.45) Median 4.5 Min, Max 3, 8 Week 16 Number Assessed NA 11 Any Gout Flares Since the Last Visit, n (%) 4 (36.4) If Yes, the following are assessed Pain different than normal, n (%) 3 (27.3) Pain at rest > 3 out of 10, n (%) 3 (27.3) Swelling in Joints, n (%) 2 (18.2) Maximum Reported Intensity of Flare (0-10 scale) [1] n 3 Mean (SD) 5.0 (1.73) Median 6.0 Min, Max 3, 6 Week 18 Number Assessed NA 11 Any Gout Flares Since the Last Visit, n (%) 5 (45.5) If Yes, the following are assessed Pain different than normal, n (%) 3 (27.3) Pain at rest > 3 out of 10, n (%) 3 (27.3) Swelling in Joints, n (%) 3 (27.3) Maximum Reported Intensity of Flare (0-10 scale) [1] n 3 Mean (SD) 6.3 (1.53) Median 6.0 Min, Max 5, 8 Week 20 Number Assessed NA 11 Any Gout Flares Since the Last Visit, n (%) 4 (36.4) If Yes, the following are assessed Pain different than normal, n (%) 2 (18.2) Pain at rest > 3 out of 10, n (%) 3 (27.3) Swelling in Joints, n (%) 3 (27.3) Maximum Reported Intensity of Flare (0-10 scale) [1] n 3 Mean (SD) 6.7 (0.58) Median 7.0 Min, Max 6, 7 Week 22 Number Assessed NA 11 Any Gout Flares Since the Last Visit, n (%) 3 (27.3) If Yes, the following are assessed Pain different than normal, n (%) 2 (18.2) Pain at rest > 3 out of 10, n (%) 3 (27.3) Swelling in Joints, n (%) 2 (18.2) Maximum Reported Intensity of Flare (0-10 scale) [1] n 2 Mean (SD) 9.0 (0.00) Median 9.0 Min, Max 9, 9 Week 24 Number Assessed NA 11 Any Gout Flares Since the Last Visit, n (%) 2 (18.2) If Yes, the following are assessed Pain different than normal, n (%) 1 (9.1) Pain at rest > 3 out of 10, n (%) 1 (9.1) Swelling in Joints, n (%) 1 (9.1) Maximum Reported Intensity of Flare (0-10 scale) [1] n 1 Mean (SD) 8.0 (NE) Median 8.0 Min, Max 8, 8 Week 26 Number Assessed NA 10 Any Gout Flares Since the Last Visit, n (%) 3 (30.0) If Yes, the following are assessed Pain different than normal, n (%) 2 (20.0) Pain at rest > 3 out of 10, n (%) 3 (30.0) Swelling in Joints, n (%) 2 (20.0) Maximum Reported Intensity of Flare (0-10 scale) [1] n 2 Mean (SD) 7.5 (0.71) Median 7.5 Min, Max 7, 8 Week 28 Number Assessed NA 10 Any Gout Flares Since the Last Visit, n (%) 2 (20.0) If Yes, the following are assessed Pain different than normal, n (%) 0 Pain at rest > 3 out of 10, n (%) 0 Swelling in Joints, n (%) 0 Maximum Reported Intensity of Flare (0-10 scale) [1] n 1 Mean (SD) 3.0 (NE) Median 3.0 Min, Max 3, 3 Week 30 Number Assessed NA 10 Any Gout Flares Since the Last Visit, n (%) 1 (10.0) If Yes, the following are assessed Pain different than normal, n (%) 1 (10.0) Pain at rest > 3 out of 10, n (%) 1 (10.0) Swelling in Joints, n (%) 0 Maximum Reported Intensity of Flare (0-10 scale) [1] n 1 Mean (SD) 5.0 (NE) Median 5.0 Min, Max 5, 5 Week 32 Number Assessed NA 10 Any Gout Flares Since the Last Visit, n (%) 1 (10.0) If Yes, the following are assessed Pain different than normal, n (%) 1 (10.0) Pain at rest > 3 out of 10, n (%) 1 (10.0) Swelling in Joints, n (%) 0 Maximum Reported Intensity of Flare (0-10 scale) [1] n 1 Mean (SD) 7.0 (NE) Median 7.0 Min, Max 7, 7 Week 34 Number Assessed NA 10 Any Gout Flares Since the Last Visit, n (%) 2 (20.0) If Yes, the following are assessed Pain different than normal, n (%) 2 (20.0) Pain at rest > 3 out of 10, n (%) 2 (20.0) Swelling in Joints, n (%) 1 (10.0) Maximum Reported Intensity of Flare (0-10 scale) [1] n 2 Mean (SD) 7.0 (4.24) Median 7.0 Min, Max  4, 10 Week 36 Number Assessed NA 8 Any Gout Flares Since the Last Visit, n (%) 2 (25.0) If Yes, the following are assessed Pain different than normal, n (%) 2 (25.0) Pain at rest > 3 out of 10, n (%) 1 (12.5) Swelling in Joints, n (%) 1 (12.5) Maximum Reported Intensity of Flare (0-10 scale) [1] n 1 Mean (SD) 8.0 (NE) Median 8.0 Min, Max 8, 8 Week 38 Number Assessed NA 6 Any Gout Flares Since the Last Visit, n (%) 2 (33.3) If Yes, the following are assessed Pain different than normal, n (%) 2 (33.3) Pain at rest > 3 out of 10, n (%) 1 (16.7) Swelling in Joints, n (%) 1 (16.7) Maximum Reported Intensity of Flare (0-10 scale) [1] n 2 Mean (SD) 4.0 (2.83) Median 4.0 Min, Max 2, 6 Week 40 Number Assessed NA 4 Any Gout Flares Since the Last Visit, n (%) 0 If Yes, the following are assessed Pain different than normal, n (%) 0 Pain at rest > 3 out of 10, n (%) 0 Swelling in Joints, n (%) 0 Maximum Reported Intensity of Flare (0-10 scale) [1] n 0 Mean (SD) Median Min, Max Week 42 Number Assessed NA 4 Any Gout Flares Since the Last Visit, n (%) 1 (25.0) If Yes, the following are assessed Pain different than normal, n (%) 0 Pain at rest > 3 out of 10, n (%) 1 (25.0) Swelling in Joints, n (%) 1 (25.0) Maximum Reported Intensity of Flare (0-10 scale) [1] n 1 Mean (SD) 8.0 (NE) Median 8.0 Min, Max 8, 8 Week 44 Number Assessed NA 4 Any Gout Flares Since the Last Visit, n (%) 0 If Yes, the following are assessed Pain different than normal, n (%) 0 Pain at rest > 3 out of 10, n (%) 0 Swelling in Joints, n (%) 0 Maximum Reported Intensity of Flare (0-10 scale) [1] n 0 Mean (SD) Median Min, Max Week 46 Number Assessed NA 3 Any Gout Flares Since the Last Visit, n (%) 0 If Yes, the following are assessed Pain different than normal, n (%) 0 Pain at rest > 3 out of 10, n (%) 0 Swelling in Joints, n (%) 0 Maximum Reported Intensity of Flare (0-10 scale) [1] n 0 Mean (SD) Median Min, Max Week 48 Number Assessed NA 3 Any Gout Flares Since the Last Visit, n (%) 0 If Yes, the following are assessed Pain different than normal, n (%) 0 Pain at rest > 3 out of 10, n (%) 0 Swelling in Joints, n (%) 0 Maximum Reported Intensity of Flare (0-10 scale) [1] n 0 Mean (SD) Median Min, Max Week 50 Number Assessed NA 3 Any Gout Flares Since the Last Visit, n (%) 0 If Yes, the following are assessed Pain different than normal, n (%) 0 Pain at rest > 3 out of 10, n (%) 0 Swelling in Joints, n (%) 0 Maximum Reported Intensity of Flare (0-10 scale) [1] n 0 Mean (SD) Median Min, Max Week 52/ET Number Assessed NA 3 Any Gout Flares Since the Last Visit, n (%) 0 If Yes, the following are assessed Pain different than normal, n (%) 0 Pain at rest > 3 out of 10, n (%) 0 Swelling in Joints, n (%) 0 Maximum Reported Intensity of Flare (0-10 scale) [1] n 0 Mean (SD) Median Min, Max End of Pegloticase Number Assessed NA 2 Infusions Visit Any Gout Flares Since the Last Visit, n (%) 1 (50.0) If Yes, the following are assessed Pain different than normal, n (%) 1 (50.0) Pain at rest > 3 out of 10, n (%) 1 (50.0) Swelling in Joints, n (%) 1 (50.0) Maximum Reported Intensity of Flare (0-10 scale) [1] n 1 Mean (SD) 8.0 (NE) Median 8.0 Min, Max 8, 8

Extent of Methotrexate Exposure (ADD 670-676 HERE)

TABLE 26 Extent of Methotrexate Exposure Period Variable ITT Population mITT Population Statistic N = 15 N = 14 MTX Run-in Period Duration of MTX Treatment (days) [1] n 15 14 Mean (SD) 23.0 (4.90) 24.1 (2.70) Median 22.0 22.0 Min, Max 8, 28 21, 28  Total Dosage (mg) [2] n 15 14 Mean (SD) 64.0 (11.98) 66.4 (7.70) Median 60.0 60.0 Min, Max 30, 75  60, 75  Any Reductions in dosage from planned 15 mg/week, n (%) [3] 0 0 Pegloticase + Immunomodulator Period Through Week 24 Duration of MTX Treatment (days) [1] n 14 14 Mean (SD) 132.2 (50.95) 132.2 (50.95) Median 161.5 161.5 Min, Max 22, 164 22, 164 Total Dosage (mg) [2] n 14 14 Mean (SD) 288.9 (112.08) 288.9 (112.08) Median 357.5 357.5 Min, Max 60, 375 60, 375 Any Reductions in dosage from planned 15 mg/week, n (%) [3] 3 (20.0) 3 (21.4) Overall Duration of MTX Treatment (days) [4] n 15 14 Mean (SD) 152.7 (63.41) 163.1 (51.02) Median 190.0 190.0 Min, Max  8, 198 57, 198 Total Dosage (mg) [5] n 15 14 Mean (SD) 333.7 (137.78) 355.4 (113.33) Median 415.0 417.5 Min, Max 30, 450 135, 450  Any Reductions in dosage from planned 15 mg/week, n (%) [3] 3 (20.0) 3 (21.4)

TABLE 27 Extent of Pegloticase Exposure in the Pegloticase + Immunomodulator Period Through Week 24 (mITT Population) mITT Population N = 14 Pegloticase + Immunomodulator Treatment Period Number of Infusions Received Overall, n (%) [1]  2 1 (7.1)  3 1 (7.1)  5 1 (7.1) 12 3 (21.4) 13 8 (57.1) Mean (SD) 10.7 (4.07) Median 13.0 Min, Max 2, 13 Duration of Exposure (days) [2] n 14 Mean (SD) 137.3 (56.89) Median 168.5 Min, Max 16, 172 Number of Incomplete Infusions Received, n (%) [1] [3] 0 Incomplete Infusions 14 (100) At Least 1 Incomplete Infusion 0 (0.0) Mean (SD) Median Min, Max Number of Infusions Received with Interruption, n (%) [1] 0 Infusions with Interruptions 13 (92.9) At Least 1 Infusion with Interruption 1 (7.1) 2 1 (7.1) Mean (SD) 2.0 (NE) Median 2.0 Min, Max 2, 2  Day 1 Infusion Number of Subjects Infused 14 Complete Infusion, n (%) [3] [4] 14 (100) Completed Infusion without Interruption, n (%) [4] 14 (100) Interrupted Infusion, n (%) [4] 0 Week 2 Infusion Number of Subjects Infused 14 Complete Infusion, n (%) [3] [4] 14 (100) Completed Infusion without Interruption, n (%) [4] 14 (100) Interrupted Infusion, n (%) [4] 0 Week 4 Infusion Number of Subjects Infused 13 Complete Infusion, n (%) [3] [4] 13 (100) Completed Infusion without Interruption, n (%) [4] 13 (100) Interrupted Infusion, n (%) [4] 0 Week 6 Infusion Number of Subjects Infused 12 Complete Infusion, n (%) [3] [4] 12 (100) Completed Infusion without Interruption, n (%) [4] 12 (100) Interrupted Infusion, n (%) [4] 0 Week 8 Infusion Number of Subjects Infused 12 Complete Infusion, n (%) [3] [4] 12 (100) Completed Infusion without Interruption, n (%) [4] 11 (91.7) Interrupted Infusion, n (%) [4] 1 (8.3) Week 10 Infusion Number of Subjects Infused 11 Complete Infusion, n (%) [3] [4] 11 (100) Completed Infusion without Interruption, n (%) [4] 11 (100) Interrupted Infusion, n (%) [4] 0 Week 12 Infusion Number of Subjects Infused 11 Complete Infusion, n (%) [3] [4] 11 (100) Completed Infusion without Interruption, n (%) [4] 11 (100) Interrupted Infusion, n (%) [4] 0 Week 14 Infusion Number of Subjects Infused 11 Complete Infusion, n (%) [3] [4] 11 (100) Completed Infusion without Interruption, n (%) [4] 11 (100) Interrupted Infusion, n (%) [4] 0 Week 16 Infusion Number of Subjects Infused 11 Complete Infusion, n (%) [3] [4] 11 (100) Completed Infusion without Interruption, n (%) [4] 11 (100) Interrupted Infusion, n (%) [4] 0 Week 18 Infusion Number of Subjects Infused 11 Complete Infusion, n (%) [3] [4] 11 (100) Completed Infusion without Interruption, n (%) [4] 11 (100) Interrupted Infusion, n (%) [4] 0 Week 20 Infusion Number of Subjects Infused 11 Complete Infusion, n (%) [3] [4] 11 (100) Completed Infusion without Interruption, n (%) [4] 11 (100) Interrupted Infusion, n (%) [4] 0 Week 22 Infusion Number of Subjects Infused 11 Complete Infusion, n (%) [3] [4] 11 (100) Completed Infusion without Interruption, n (%) [4] 11 (100) Interrupted Infusion, n (%) [4] 0 Week 24 Infusion Number of Subjects Infused 8 Complete Infusion, n (%) [3] [4] 8 (100) Completed Infusion without Interruption, n (%) [4] 8 (100) Interrupted Infusion, n (%) [4] 0 

What is claimed is:
 1. A method of treating gout in a patient having a serum uric acid (SUA) level of ≥6 mg/dL comprising: administering methotrexate (MTX) to said patient at a dose of about 5 mg to about 50 mg per week for a period of 4 weeks prior to a first administration of a PEGylated uricase; and co-administering the PEGylated uricase and MTX to said patient using a dosage regimen comprising a dose of about 0.5 mg to about 24 mg of the PEGylated uricase intravenously every 2 weeks for a total of 26 doses, and a dose of about 5 to about 50 mg of MTX per week, wherein the co-administered MTX is administered concurrently with each administration of the PEGylated uricase.
 2. A method of reducing immunogenicity to PEGylated uricase and prolonging the urate lowering effect comprising co-administering a PEGylated uricase at a dosage of about 0.5 mg to about 24 mg intravenously every 2 weeks and methotrexate (MTX) at a dosage of 15 mg per week to a patient having a serum uric acid (SUA) level of ≥6 mg/dL prior to PEGylated uricase treatment initiation, wherein the administration of the PEGylated uricase and MTX result in the SUA level being reduced relative to a patient not receiving co-administration of the PEGylated uricase and MTX immunosuppressive therapy.
 3. The method of claim 1 or 2, wherein the PEGylated uricase is administered at a dose of 8 mg and MTX is administered at a dose of 15 mg.
 4. The method of any of claims 1 to 3, further comprising administering folic acid to said patient at a dosage of 1 mg per day.
 5. The method of any of claims 1 to 4, further comprising an altered dosage of MTX, wherein the altered dosage comprises: administering folic acid to said patient at a dosage of about 2 mg per day; or administering MTX to said patient at a dosage of about 7.5 mg twice per day; or administering MTX to said patient at a dosage of about 10 mg, wherein the altered dosage of MTX is based on laboratory findings.
 6. The method of claim 5, wherein the altered dosage of MTX comprises a temporary stop for laboratory parameters selected from the group consisting of WBC levels of less than about 3.0×10⁹/L, platelet levels of less than about 50×10⁹/L, hematocrit levels of less than about 27%, AST/ALT levels of greater than about 2x upper limit of normal (ULN), and eGFR levels of less than 30 mL/min/1.73 m², wherein the altered dosage of MTX comprises a reduction in the dosage of MTX to 10 mg per week for laboratory parameters selected from the group consisting of: WBC levels of from about 3.0×10⁹/L to about 3.5×10⁹/L and AST/ALT levels of between about 1.5 and about 2× ULN.
 7. The method of claim 1 or 2, further comprising a prophylactic regimen of colchicine for a period of at least 2 weeks prior to the first administration of the PEGylated uricase.
 8. The method of any of claims 1 to 7, wherein the SUA levels of the patient are determined prior to each dose of the PEGylated uricase.
 9. The method of any of claims 1 to 7, further comprising measuring one or more of trough PEGylated uricase levels, anti-PEGylated uricase antibody levels, and anti-PEG antibody levels, prior to each dose of the PEGylated uricase after the first dose.
 10. The method of claim 2, further comprising measuring hematology and liver function during treatment.
 11. The method of any of claims 2 to 10, wherein said co-administration of the PEGylated uricase and MTX results in normalization of the SUA level in the patient relative to a patient not receiving co-administration of the PEGylated uricase and MTX immunosuppressive therapy.
 12. The method of any of claims 1 to 11, wherein the SUA level is reduced to less than 6 mg/dL as a result of co-administration of the PEGylated uricase and MTX immunosuppressive therapy.
 13. The method of any of claims 1 to 12, wherein the SUA level is reduced to less than 5 mg/dL as a result of co-administration of the PEGylated uricase and MTX immunosuppressive therapy.
 14. The method of any of claims 1 to 13, wherein the SUA level is reduced to less than 2 mg/dL as a result of co-administration of the PEGylated uricase and MTX immunosuppressive therapy.
 15. The method of any of claims 1 to 14, wherein the incidence of infusion reaction, gout flare, or anaphylaxis is reduced as a result of co-administration of the PEGylated uricase and MTX immunosuppressive therapy.
 16. The method of any of claims 1 to 15, wherein the level of MTX metabolite is increased relative to a patient not receiving co-administration of the PEGylated uricase and MTX immunosuppressive therapy.
 17. The method of claim 1 or 2, further comprising measuring one or more of peripheral joint urate deposition volume and inflammatory volume via any advanced imaging technique.
 18. The method of claim 17, wherein peripheral joint urate deposition volume is reduced in the patient relative to a patient not receiving co-administration of the PEGylated uricase and MTX immunosuppressive therapy.
 19. The method of claim 18, wherein peripheral joint urate deposition volume is determined by dual-energy computed tomography (DECT) scanning.
 20. The method of claim 19, wherein peripheral joint urate deposition volume is determined by ultrasound.
 21. The method of claim 17, wherein inflammatory volume is reduced in the patient relative to a patient not receiving co-administration of the PEGylated uricase and MTX immunosuppressive therapy.
 22. The method of claim 21, wherein inflammatory volume is determined by Dynamic Contrast Enhanced Magnetic Resonance Imaging (DCE-MRI), or MRI without contrast, or both.
 23. The method of any of claims 1 to 22, wherein the mean titer of anti-PEGylated uricase antibodies is less than or equal to 1:6000 as a result of co-administration of the PEGylated uricase and MTX immunosuppressive therapy.
 24. The method of any of claims 1 to 23, wherein the serum uric acid level is normalized by week 12 after co-administration of PEGylated uricase and MTX treatment begins. 